Understanding Automotive Electrical Schematic Diagnosis - For Beginners and Do it Yourselfers | Steven Liguori | Skillshare

Playback Speed

  • 0.5x
  • 1x (Normal)
  • 1.25x
  • 1.5x
  • 2x

Understanding Automotive Electrical Schematic Diagnosis - For Beginners and Do it Yourselfers

teacher avatar Steven Liguori, Teaching is My Passion

Watch this class and thousands more

Get unlimited access to every class
Taught by industry leaders & working professionals
Topics include illustration, design, photography, and more

Watch this class and thousands more

Get unlimited access to every class
Taught by industry leaders & working professionals
Topics include illustration, design, photography, and more

Lessons in This Class

24 Lessons (2h 7m)
    • 1. Welcome and Introduction

    • 2. 02 Voltage Current Resistance

    • 3. 03 What Every Circuit Needs

    • 4. 04 What Every Circuit Needs Applied to a Schematic

    • 5. 05 Power Load Ground Can it Be this Easy

    • 6. 06 Power Load Ground Explained Using Schematic

    • 7. 07 Diagnosing an Inoperative Circuit

    • 8. 08 Four Types of Faults

    • 9. 09 Series and Parallel Circuit Differences

    • 10. 10 Voltage At Worksheet 2 Bulb Series Circuit Switch Closed

    • 11. 11 Voltage At Worksheet 2 Bulb Series Circuit Switch Closed Answers Explained

    • 12. 12 Voltage At Worksheet 2 Bulb Parallel Circuit Switch Closed

    • 13. 13 Voltage At Worksheet 2 Bulb Parallel Circuit Switch Closed Answers Explained

    • 14. 14 Series Schematic Variations

    • 15. 15 Schematic Wiring Differences

    • 16. 16 Brake and Park Lamp Circuit

    • 17. 17 Brake and Park Lamp Fault 1

    • 18. 18 Brake and Park Lamp Fault 2

    • 19. 19 Horn Schematic Circuit Explained

    • 20. 20 Horn Schematic Additional Schematic Details

    • 21. 21 Horn Schematic My Horn Sounds Like a Sick Cow

    • 22. 22 Horn Schematic Horn Inoperative

    • 23. 23 Horn on all the Time

    • 24. 24 Thank You

  • --
  • Beginner level
  • Intermediate level
  • Advanced level
  • All levels
  • Beg/Int level
  • Int/Adv level

Community Generated

The level is determined by a majority opinion of students who have reviewed this class. The teacher's recommendation is shown until at least 5 student responses are collected.





About This Class

Automotive Service Excellence (ASE) Master Technician and Instructor Steve Liguori, Teaches Beginners, and Do-it-Yourselfers how to Understand Automotive Electrical Wiring Diagrams and Schematics.  He Demonstrates a Process that can Promote Quick and Accurate Diagnostic Results.

The Achievable Goal for Some Students will be to Diagnose their own Vehicle's Electrical Problems.  For Others, the Knowledge Gained from Practicing what is Taught in this Program will allow them to Narrow Down the Possible Causes for a Fault they are Experiencing, as well as give them the Confidence to Recognize if the Service Center they utilize is Honest and Competent.

The more you practice what is taught in this course and Apply the Process to various wiring diagrams on your car, the more Comfortable and Proficient you will become.  This course explains the foundation material necessary to Understand many Basic Electrical Circuits.

Having Educated Thousands of Students over the years, Steve has found a way to Cut to the Chase and provide large amounts of understanding in a small amount of time.  Spend a couple of hours Learning, Reviewing and Practicing the Principles in this Course and you will be well on your way to the Basic Automotive Electrical Understanding You Desire!

Meet Your Teacher

Teacher Profile Image

Steven Liguori

Teaching is My Passion


A Tale of Two Careers….


Steve has been trading Stocks and Options since 1999.  With his passion for teaching, he has been a perfect fit as an Options Coach/Mentor for three Online Trading Education Companies.  The Founder and Options Coach at BlueChipTraderDevelopment.com, Steve is available to answer your questions as well as provide One-on-One Online Personal Coaching Sessions.

Years of Coaching new and experienced Traders has given Steve the understanding of what struggling traders need most, clear explanations of the Processes that will lead them to the Success they are looking for in their Trading.


Prior to becoming a Full Time Trader, Steve was and still is an ASE Certified Master Automotive Technician.  He was... See full profile

Class Ratings

Expectations Met?
  • Exceeded!
  • Yes
  • Somewhat
  • Not really
Reviews Archive

In October 2018, we updated our review system to improve the way we collect feedback. Below are the reviews written before that update.

Why Join Skillshare?

Take award-winning Skillshare Original Classes

Each class has short lessons, hands-on projects

Your membership supports Skillshare teachers

Learn From Anywhere

Take classes on the go with the Skillshare app. Stream or download to watch on the plane, the subway, or wherever you learn best.


1. Welcome and Introduction: Welcome to the do it yourself. Automotive electrical diagnostic program. My name Steve allegory. I'd been amassed our automotive technician for over 35 years and I've worked in dealerships for over 25 years, mostly as an electrical specialist. It was my job to diagnose the problems that most people had trouble fixing or finding out what was wrong with. What I want to try and do in this course is give to you some of the shortcuts and understanding of electrical that I have so that you can use it to identify information on a schematic and saved the amount of time that you need to spend working on the car? I can't tell you how many times I would get a repair order would say the blower motor doesn't work. The first thing I would do is walk over to the computer and print out the schematic that is for that particular model. And then I would walk over to the car to verify what the concern was, spending five minutes sitting and looking at the picture and understanding what the possibilities were. There were times that there was only one possibility of what could be wrong where I could walk over to the parts department without even bringing the car in and say, Do you have a blower motor resistor in stock for this particular model? And if that was the case, I could go right back up to the service desk and tell them with the car needed and sometimes don't even have to make a test on the car as long as I've already verified that the condition was there. Now it's not always that simple, but there were times that that's all it took. And other times I could narrow down 50 percent, 75 percent of the circuit just by spending a little time looking at the schematic and understanding how that particular circuit work. And that's the part that I'm trying to give you in this course and understanding so that you'll narrow down for yourself. Sometimes you just need to go out to the car, verify the concern, find the proper schematic for the car, and spend a little time with it. And it's true that in the beginning it's going to take you more time than it took me. But with practice, you'll wind up getting good at this and you'll find that you'll be amazed at how easy it can be. Now if you're going to be repairing your own car on your own, it's going to require you're taking some type of a hands-on course to make sure that you have the skills and the safety precautions necessary to do that. So I would be careful with jumping right in and testing something on your car until you're comfortable and feel you've acquired the skills to do that part in this course, what I'm going to give you is that understanding of the picture and a way to help you diagnose and understand what the possibilities are. You're going to work like a detective where electrical diagnosis is a process of eliminating all of the potential suspects until there's only one left, and then that person has to be guilty. And in this case the person would be whatever component or wire that's causing the problem. So with that said, let's get started. 2. 02 Voltage Current Resistance: even though this course is not meant to be a college program where they might spend months on theory of electricity and atoms and electrons and protons, we still have to cover some basic electrical definitions so that you can understand how we can apply them to schematic diagrams and diagnostics. We are going to cover voltage, current and resistance and some other terms as we move forward, so that we can have a basic understanding of these terms and apply them to the real nuts and bolts of what we're trying toe learn here, which is how to diagnose our own car or diagnosis using a schematic. So that will be much more aware of what a particular problem might be when we have certain conditions or certain devices on our car not working. So let's start with voltage. Voltage is the electrical pressure or force that pushes electricity through an electrical circuit. It's measured in volts. We use a volt meter to measure voltage, and it's represented by the Symbol E and some books. If you were doing the math on the circuits, would use the Symbol V, and we're not covering any of the math in this course, but there may be courses in the future that I will make depending on the demand for them, which will cover the math part in debt. Some people want to know, but most people really want to just understand. What do I need to know? To diagnose my car were to understand what I'm doing as far as looking at a schematic diagram, and that's what we're really trying to cover here. So now current current is the flow of electricity. It's actually the movement of electricity through a circuit where voltage is the pressure. Let's think of voltage as you're looking at the Apple store, and they just released the new iPhone. Everyone's waiting for the store toe open, and there are hundreds of people pressed up against the front door of the store waiting to go in. That would be people pressure so electricity or electrical has voltage, which is electrical pressure. This would be an example of people pressure, but there is no current flow yet because the store is not open and there's no complete path for them to get inside. In order to have current, we would have to open a door to the store, and then we would have people current. The amount of people flowing past a certain point in one second would be how many people are flowing in electricity. It would be measured in amps, and it's a measurement of how much current is passing a point in the circuit in one second . So getting back to our apple store, if we open a small door, we might have one or two people going past a certain point in one second. And if there was more pressure outside the store, like lots and lots of people forcing each other to go through, we might even get three or four people to go through the door in one second, depending on the size of the door. And this is where the third term resistance comes in. Resistance is the opposition to current flow, something that causes a restriction or inhibits current flow. If I have a circuit that has low resistance, that will allow higher current flow, and if I have a circuit that has high resistance, that will create a condition where we will have lower current flow. Resistance is measured in homes and is represented by the symbol are But to understand it better, let's get back to the Apple store. What would happen if they now open to second door or the second of a double door? Now more people could flow inside, so the resistance to getting inside is now less, which increase the current flow. And this is the same way it works with electricity. If we have a decrease in resistance, current flow increases and if we haven't increase in resistance than current flow decreases . So it is important to understand that relationship. But it's not necessarily that important to go through a college course on all of the math and the theory behind it, just so that you can diagnose your car. 3. 03 What Every Circuit Needs: every electrical circuit on the car really just needs three things. In order for the circuit to operate, we need to have a power supply, which would be the battery or the alternator. When the car is running, we need the power side of the circuit, which includes the supply wiring all the way up to the load. The load of the circuit is the part of the circuit that's designed to operate or use the voltage. So an example of that would be the horn or the headlights or the tail lights or the blower motor, the starter motor, all of those air loads. The third thing that we need in order for a circuit toe work is the ground path, and the ground path includes the wiring from the load back to the battery, and this can also include the metal frame of the vehicle, often times and in many or most cases, the metal frame of the vehicle is used for the ground path because it eliminates the need for extra wiring all the way back to the battery for each particular circuit on the car. If you use the metal frame of the car, it eliminates some of the wiring that you might have to run, which anything that they can do to eliminate wait can increase gas mileage and performance , so that's why they do it. 4. 04 What Every Circuit Needs Applied to a Schematic: in the last video, we talked about the three things that every circuit needs. There's actually two more things that automotive circuits use. They don't need them for the circuit to power up. For example, these bulbs would like if I didn't have a switch and if I didn't have a fuse. But by adding these two components, we actually add protection, which is what the fuse does. And we had a way of controlling the device to be on or off when we want to. Now, electrically speaking, if both of these devices were not there, we could then just have a circuit that works. So what we need for a circuit toe work is the power supply, the load and the ground path. So in this picture, the power supply part of the circuit would be from the positive battery all the way up to the positive side of the bowl. So that's the power supply, which includes the battery or the alternator and the circuit wiring up to the load. And this is also in this picture, including the fuse in the switch, and then we have the load part of the circuit. The load part of the circuit is where the voltage gets used up. In this case, the load part of the circuit is two bulbs that Aaron Siri's. So these two bulbs are actually going to share the voltage because of the way Siri's circuits work, and the load part would be from here to here. So this is the area of the circuit where we would expect all of the voltage to be used up. The third part of the circuit is the ground path, and that's the other part that's required for the circuit to operate. And that would be the part of the circuit, in this case, from the negative side of the bulb, all the way back to the battery to the negative terminal. In the next video, I'm going to show a short dramatization of how easy the diagnosis of this kind of a circuit or of any basic electrical circuit can be. If you understand that there are only these three parts and our job is to find out which one of these three is either missing or faulty, so I'll see you in the next video 5. 05 Power Load Ground Can it Be this Easy: Now that we know that every circuit requires power, load and ground, our job is to find out which one is missing. When we're diagnosing a circuit, that is our main goal. Which one is missing or defective? Let's take a look at this and see how easy it can be imagined that this is a circuit the words power load and ground. And I'm going to put a fault in one part of the circuit and see if you can tell which one is missing. Okay, So where is the fault? Is it the power that's missing? Is it the load or is it the ground? This seems too easy. Let's try that again. Here we are with our power load and ground again. And I'm gonna put another fault in the circuit, See if you can figure this one out. So which one is missing? Is that the power? Is it the load or is it the ground? Come on, it can't be this easy. Let's try one more time. Here we are again with our working circuit power load and ground. Let me put one more fault in this and see if you can figure it out. So obviously it's the ground that's missing this time. While this seems like a little silly exercise or activity, what if I told you that there was a simple voltage measurement that you could make to determine if the power side of the circuit is missing or if it's defective and the same with the ground side? You could determine if the ground side of the circuit is missing or defective. What if you could use a volt meter? Then you be able to isolate which one of these is missing. And it's not as hard as it seems in the upcoming videos. I'm going to show you how you can easily figure out from a picture or schematic. You'll have a circuit that's not working. You know now that it's gonna be either power loader ground that's missing or defective, and you will be able to make a test or two. Usually it takes no more than one or two or three tests, and in some cases you can almost diagnose the whole problem just from the picture, based on what other devices on the car are already working. Or if they may also have a fault. As we move into the next video. I'll show you examples of power load and ground on a schematic and what they would look like. And then we'll get into what volt meter readings will tell us which one of these a rate fall. 6. 06 Power Load Ground Explained Using Schematic: Let's use a schematic this time to demonstrate how we can identify, which is missing power, load or ground. Remember from a previous video that the power side of the circuit is everything from the positive battery terminal up to the positive side of the load. Or, in this case, the first bolt and load is everything from where the first load starts to where the last load ends. So if there is more than one load in the circuit load, part of the circuit is where the voltage is going to get used up. And if there was only one load in the circuit or one bulb, the load part of the circuit would just be from here to here. But in this case, the load is from here to here because the two loads Aaron Siri's and that's where the voltage gets used up. And then there's the ground path that goes from the negative side of the last load in the path, and it goes all the way back to the negative battery. Let me show you a few examples of what it would look like if there was a fault. That was the power side missing or defective or the load missing or defective or the ground path missing word effective. So let's start with power. So now we can see that the power side is definitely at fault here because the word power is missing. But what does that mean on the picture? Well, for one thing, it means that the bulbs air, not let anymore. The switch is still closed, so it looks like everything should be working. But something is not working. And this is how most situations come into a shop or whenever something happens to your own personal car. This is what you get. You've operated to switch the way you normally do, and you don't get the result you want lighting up the bulbs or whatever the devices. And if power was missing, what it means is there is a fault either an open or a high resistance problem or something defective or missing in the power side of the circuit. The problem could be anywhere in this path that, we determined, was the power side on this particular picture earlier. It could be that it's just in this wire. There could be a break in the wire or corrosion here. It could be that the switches physically closed, but internally this which is defective where maybe there's an opening it. It could be that the wire between the fuse and the switches bad. It could be right here. Or it could be over here in this location, and it could be even before the fuse or the fuse itself. So maybe there's an open circuit here, a break in the wire, and maybe there's something else that's wrong, which is a short to ground, perhaps right here, which caused the fuse to blow, which then interrupted the power circuits. So even though we had a short to ground, we wound up blowing the fuse, which created an open which now is no longer allowing the voltage from the battery to get where it needs to go. If the load was missing, then it could be that there's just a fault in the wire between the two loads. Or it could be one of the loads themselves. Perhaps bold number one is blown out or bold. Number two is blown out. The situation would be the same thing. We'd have a circuit that's not working. We have power applied to it. The switches on none of the bulbs, air lighting and we would make a test and find that the power circuit is good and we'll talk more about what readings we would need to see to tell us that the power circuit is good. Once we determined that the power side of the circuit is good, then we would go and test the load part of the circuit. So the third thing that we talked about earlier was that the ground could be missing or defective. Let's take a look at what that might look like on this matter. So here we are again and we can see that the ground is missing over here, the word ground. But what would that look like on the picture? It could be that there's a break in the wire, the ground path right after the bull, but could be right near the bulb. It also could be somewhere along the path on the way back to the battery. It could be right here, could be right here, and it could be right over here. So there are readings that we can make that will tell us if it's the power side if it's the load, and if it's the ground side, it's much simpler than you think. Once you understand what you're looking for on the picture and understand what the different readings mean, your job becomes very easy. 7. 07 Diagnosing an Inoperative Circuit: diagnosing in an operative circuit. It comes down to answering these three questions. What voltage do I expect to expect Battery voltage to expect zero volts or somewhere in between? Question number two. What voltage is present? What voltage reading do I get when I measure at a certain location in the circuit and then question number three? What does it mean? Does the volt meter reading I get indicate that there's an open or high resistance? Or is the reading normal? And I have to check somewhere else, either further back or further down the line in the circuit. Based on the reading that I get the upcoming videos, we're going to practice on Siri circuits than parallel circuits and then more complex circuits so that we understand how to determine what to expect so that if we do make a measurement on the car, will know what it means, and we'll know what to do with it. Like I've said earlier, you will be amazed at how fast and easy your diagnosis can be. The hardest part on occasion is accessing an area of the circuit on the car that might be hard to access, so that could be an issue, but the knowledge that you get from this program can help you determine if the place where you bring your car is treating you properly. You you can look at a picture and then bring the car in and let them do the work. But you'll have enough knowledge to know if what they tell you that you need makes sense or not based on the picture and based on your understanding of how the circuit works, You can save money either way, either by doing it yourself or just by understanding or just by knowing if the people you have working on your car actually know what they're doing. 8. 08 Four Types of Faults: There are four types of faults that can affect the way a circuit operates the 1st 1 and the most common one is an open circuit, which is just a disconnected wire or disconnected component or a physical break in the wire somewhere along the path in the circuit, high resistance can sometimes act just like an open circuit in what it causes, because high resistance sometimes causes the circuit not to work at all, but often times it just allows the circuit to not work properly or intermittently. For example, if we were talking about an open and open could be a physical break in the wire or a physical break inside the switch contacts, which would cause the circuit not toe work. But high resistance would be corrosion on the switch contacts, which instead of it not allowing the voltage to get to the bulb. It might allow some of the voltage to get to the bulb, which would cause the bulk to operate abnormally. And if the high resistance or the corrosion on the switch contacts was severe enough, then it might rob so much of the voltage from getting to the bulb that the bulb would be in operative completely so that it would seem like it was similar to an open circuit. But there's a definite difference between an open and high resistance. And when we learn what the meter readings are for these different areas of the circuit, what the normal reading is and what's wrong if we don't get the normal reading, depending on what that reading turns out to be, will tell us if we have an open or a high resistance problem. Short, devoted and short to ground, those are a little different. These can cause different kinds of conditions than an open and high resistance. Open and high resistance can cause the circuit, not toe work. But short to voltage can often cause a circuit toe work when it's supposed to be off. So looking at our picture over here on the left, if I had a short to voltage over here on this wire, so just picture that this wire is rubbing up against another wire that has 12 volts on it, and over time the two wires have rubbed each other to where the 12 volts that was on the one wire that's normal toe have that voltage has worn off the insulation on another wire next to it in the harness. And now that 12 volts is touching this wire, that should have no voltage on it right now. While this which is open and what it's doing is it's sending the voltage to the lamps, and these two bulbs are just going to use up the voltage because there's already a ground path. A short voltage would cause a fault where the bulbs are on when we don't want them on. Or perhaps it would be the blower. Motor stays running when your car turns off for the cooling fans days running and drains your battery when the car turns off. Now, in the case of the cooling fans, many manufacturers have a a way of leaving the cooling fan on for perhaps five minutes to help cool the engine if it's in an overheat condition. But that would be normal, and that's done with some electronic circuitry. When we're talking about short voltage causing something to be on, we're talking about something to be on that we don't want on anymore. Now, short to ground, short to ground is where you have a connection to ground where you don't want one. If I had a short to ground on this wire that's already touching ground, that would be a fault. But it would be a fault that wouldn't actually even cause anything, because this wire here is supposed to be connected to ground. So this is a case where the wire could be shorted to ground, but because it's already connected to ground, it would cause no problem. But what if the wire up here was shorted to ground or rubbed through the insulation on this wire to a piece of metal? If we had a ground path over here to ground, what it would do is it would burn up this wire. This wire would go up in smoke because if you try to take a high powered battery, that could deliver a lot of current, and you try and put it through a device that does not have any resistance. It's the resistance that we learned briefly in the beginning of the program that decides how much current will flow in the circuit. So the bulbs here have a certain amount of resistance which will limit the current flow. And if the current flow becomes excessive than the fuse blows. And that's why we have this fuse there as a protection in case there is a short to ground. But if the short to ground happens before the fuse, there's no protection there. So if the positive battery cable or any wire that has no protection until you get to the fuse was to rub through to the metal on the car, you would actually have a wire that has almost no resistance or so small that it would not limit the current flow very much at all. And it would actually create a path as if it went through this piece of wire and right back to the battery, almost as if you shorted out the battery with a piece of wire. And what would happen is that wire, because of its low resistance, would try to draw as much current as the battery is capable of delivering. And a car battery is capable of delivering a enormous amount of current 800 to 1200 amps or even more in some cases. And what it would do is it would just like that wire on fire because that wire couldn't handle the heat that would develop because of its small physical size, it would be able to handle it, and it would just it would just melt. It would just go on fire. So this is definitely a dangerous situation, which is why you should never lay any tools across the top of a battery. Because if they accidentally touch the negative and the positive terminal with your tool and it was metal, it would actually do the same thing that a shorted wire across the battery would do. That tool could possibly just try to draw so much current that it could actually disintegrate. But what if the short to ground now was after the fuse? What would that actually cause we have the protection that we want the fuses there to protect the circuit, unlike if the short was before the fuse were could cause a fire or melt the harness if the short to ground is after the fuse. What we're gonna have is we're gonna have a situation where we have a complete path all the way back to the battery now, because this wire is touching ground. So it's a Ziff. There's a complete bath back to the battery, and what that's going to do is it's going to try to draw that enormous amount of current that we were talking about a minute ago. But the fuse, which says 20 amps as soon as the current exceeds 20 amps, the fuse will blow and create an open circuit where the fuses so that the current will stop flowing. And we don't have this situation that could be dangerous anymore. We still have a situation where the circuits not working and the circuits not working because of the open in the fuse. But putting a new fuse in doesn't fix the cause of the problem. All it does is put another fuse in, so that if that wire rubs and touches ground again, the exact same thing will happen. And this is why a lot of times people have a condition on their car where the fuse blows and they put the fuse in, and they think that everything's repaired, but nothing's really repaired. It's just a temporary fix until that wire rubs hard enough on a piece of metal toe, where it creates the short to ground again. Now, in some cases, the fuse when you go to put a new one and it'll blow right away. And if it does, it means that that wire is still shorted to ground, and you're gonna have to find where that wire is rubbing or touching the metal and get it to not touch the metal anymore. Otherwise you're gonna have that fuse blow either intermittently or right away. Now, one other place where we could have the fuse blow, which will make the circuit not work at all, would be after the switch. But in this case, it's a little bit different than if it was before the switch. If it's before the switch, I would blow the fuse. Let's say the fault is there right now. If it's before the switch, I would blow the fuse as soon as I plugged a new fuse in. However, if the short to ground was on the wire after the switch, then as long as the switches open, I might come to the car and find that the fuses blown and there's an open here and inside the fuse. So I replaced the fuse, but the circuits currently in the off position, so I'll put the fuse in and the circuit won't blow the fuse again yet. But as soon as I go to operate the device, the bulbs, the switch that controls the bulbs, then the fuse will blow because this wire after the switch is touching ground, and understanding all of this will help you with your diagnosis. If you were trying to diagnose a circuit that has a blown fuse, if you were to put a fuse in and the fuse blew right away, then you would be able to determine that the fault would have to be between the fuse and the switch if the switch was in the open position. But if it only blue after you closed the switch to operate the device, then the problem is not between the fuse and the switch, and it's definitely not between the battery and the fuse. In that case, it would be between the switch and the bulb. So the more you understand about the types of faults and understanding the schematic diagram, you will be able to isolate and narrow down what the possibilities are of what's causing your problem in a very short amount of time. Now there's one last thing that can also happen. What if the short to ground was right here in between the two bulbs now normally in a series circuit that has two bulbs in it? They're going to share the voltage. So the 12 volts is going to get split between these two bulbs, where they would each get six folds to operate, and the bulbs would be dimmer than they would be is if they had bubbles each. But if I had a short to ground here, that would mean that 12 volts would be getting to the positive side of this bowl. But because there's a short to ground after the first bulb, there's a path all the way back to the battery now to the negative terminal just through this bulb. So what's gonna happen? His bulb one is gonna be bright and bulb number two will not be on it all because bold number two is connected to ground on one side and it's connected to the short to ground that's on the other side. So what we would have is we would actually have a complete path through the first bowl, and the second bulb would not get any voltage because there's a return path to ground before you get to the second bowl. So a short to ground can cause quite a few different scenarios based on where the location of the short to ground is. And sometimes for some people, that's the hardest one to deal with. And the more you understand the picture and understand the principles of how the circuit works, you'll be able to tell based on what the condition is based on. If you put the fuse in and then it blows. What if it melts the wire? What if this bulb is operating? But this one's not and this one's brighter than normal, you'll be able to tell what type of issue you have. And if this bulb is on bright and this one's off, that means that this bulb is getting 12 here and zero here, so that means you have a ground from here. Teoh. Here something is shorting this to ground or inside this bold. This bulb could also be shorted, so let's say the load itself is now shorted toe where that's providing the full ground path all the way back to the battery, which would allow this bulb to be bright and this bulb to be off because it shorted. Now, if this ball bulb number two was open, then neither bulb would work because there would be no path going all the way back. But if this bulb is shorted to ground or this wire is shorted to ground, then bolt number one would be bright and bold. Number two would be off. So you might want to look through this video once or twice and just pause it to try and digest the information and the locations I'm talking about on the picture and see if you can understand them a little bit. As we go through the diagnostics on some different schematics in later videos, we're going to bring these up several times so that we can cement in what the different readings and the locations will mean. And once once you get the understanding down, then you just have to apply it to the different circuits, and as we move forward, you'll find that it becomes easier and easier and easier 9. 09 Series and Parallel Circuit Differences: in this video, we're gonna go over the differences between Siri's and parallel circuits. We're going to keep the explanation simple so that we don't make this course to complex. In this course, I'm trying to get you to understand how to read schematics, how to use your knowledge of reading schematics and then anticipating what the voltages would be in different parts of a circuit to help you diagnose and reason out what could be wrong or could be right. Actually, when you're diagnosing your really eliminating the things that are good and narrowing it down almost like your detective toe, where you then have the part of the circuit that's left that will wind up being guilty. So on the left here, I have to Siri circuits. The top circuit is showing an open circuit. Noticed that the switch is open on the bottom picture. I have to switch closed and notice that the bulbs are lit now. Noticed that on the left the bulbs are lit a little bit dimmer than they are in the pictures. On the right. On the right, I have a parallel circuit, and again I have a switch and this one switch if it was turned on, would control both of these bulbs. So in the bottom picture, I'm showing this which closed? Notice how both of the bulbs are lit and notice also that they're lit brighter than the bulbs are in the series circuit. So this brings us to our first difference between Siri's and parallel circuits. The first differences if you use a serie circuit and use multiple loads or multiple bulbs, whatever the devices that you're using. Bulbs. Resistors. So what happens here is when we want to have to. Devices use less than 12 volts. We put them in a series circuit so that they share the voltage. So one example of this would be on daytime running lights. Some manufacturers will wire the bulbs in Siris so that they share the voltage and then because they're sharing the 12 volts, let's say they're sharing it equally. That would mean that this topple would get six volts and the bottom bold would get six polls. So because of that, the amount of the voltage that the bulb is actually getting is gonna factor into how bright that bulb will be. And in the parallel circuit, the reason that a parallel circuit is used more often in automotive is that we want each individual circuit that were operating most of the time, like the blower motor or the radio or the window motor or the door locks. They're all 12 volt circuits, and we want them to each have their own 12 volt circuit, so they wire. Most of the most of the schematics, and drawings on the car are in parallel because we want each device to be able to have that 12 volts available. But for the cases where we do want them to have less voltage, one of the ways that they'll do it is by putting things in Siris. There's also a device called a resistor that you could put into the picture toe, where if I put a resistor in this picture right here on this parallel path of this one bulb , the resistor would use up some of the voltage, and the ball would use up some of the voltage. So if I didn't want to put the two bulbs in Siris, I could then add in a resistor in part of the circuit where I wanted it to be dimmer or I wanted this voltage to be less up here, and that would also do the same thing. The main difference here that we're referring to for Siris in parallel circuits is Syriza's , used when we want them to share and series circuits means Onley. One path and a parallel circuit is used when we want each device toe, have 12 volts available to it and noticed that a parallel circuit is just made up of a couple of Siri circuits where a part of the circuit is shared. If I was to draw a line from here and went all around the path through this first bulb, notice how I could come back to the battery and if I just looked at the part that I just highlighted, that's a serious circuit. And let's say I was gonna make a separate Siri's circuit where I'm doing the same thing, but this time only for bold, too. So if I then highlight this picture coming around here and down and all the way back, and I just ignored this for now, wouldn't that also be a second series circuit? So a parallel circuit is just where we're putting to Siri circuits orm or together where a part of the circuit is similar. So in this picture they're using the same battery. They're using the same fuse. They're using the same switch. But there's a point where the circuit splits. And then there's a point where it comes back together. And the good news for this is in a parallel circuit. If this is a 12 volt circuit, each of these branches of the circuit or legs of the circuit, as they're sometimes called, has 12 volts available to it, which is why these bulbs are bright and the other good part about a parallel circuit, which is most important, is if there was a fault in here, for example, an open circuit that makes this bulb go out, then this side, this path or this leg of the circuit would not be affected as long as the open is inside this branch or inside this path. Now, if I had an open in the circuit that was over here, that would affect this bulb. But it wouldn't affect that bull because the full path for this bulb is still intact Now, in 1/3 scenario, if I had an open down here in the ground path that was on the way back to the battery. This ground path is needed by each of the pats, the path for bold one and the path for bulb to. So if there was an open in this part of the circuit, that would actually affect both bulbs in the same way that if the fuse was blown, it would affect both bulbs because that would be just a Ziff. There's an open in the part of the circuit that they both need. So the disadvantage to Siri's is that if there's a fault anywhere in the circuit, then the whole circuit becomes dead. But in a parallel circuit, as long as the fault is in a particular section of the circuit than it won't affect all of the other devices and on a car. What they do is they branch out in a tree form from the battery toe, where you would have the battery feed a bunch of different fuses, and then each fuse would have its own path with certain devices on that path, so that each fuse then would be allowing the 12 volts to go to the different circuits on the car so that if one fuse blew on the car wouldn't affect the others. The parallel circuit is used extensively in automotive because it allows the two main concepts it allows each branch of the circuit to have the full voltage. And the second main big difference and big deal that we need is that if there's a fault in one of the branches, it won't affect the other. 10. 10 Voltage At Worksheet 2 Bulb Series Circuit Switch Closed: in this schematic example, I want you to try and figure out what each of these meters meter one through meter eight would read if the circuit was working normally. So what I have here is a 12 volt battery. This is a battery schematic symbol, and then I have a fuse, a switch and two bulbs and the two bulbs. Aaron Siri's. So the circuit itself is just this part here, coming all the way around and then back to the battery. And then I have the meters. Each of these is a volt meter where this is the red lead and the red lead is being connected here on the one side of the fuse. And in the second meter, the red leaders being connected on the other side of the fuse and the black lead of the meter is connected to ground or metal on the car or the negative battery terminal. So when you see the ground symbol, it just means that than negative lead of the meter is connected to a good ground, be it the middle of the car or the negative battery and the positive lead or the red lead is being connected toe a part of the circuit to measure how much voltage is available at that point. So some people will call this a voltage at measurement or seeing how much voltage is available at a specific point. So there are eight meters in this picture, and I want you to pause the video and try and figure out what you think these readings should be if the circuit is working normally. So what should be the reading on the meter at this point at this point? A point number three before the switch at point number four after the switch, when the switch is closed and then again, the positive side of the first bold, the negative side of the first bolt, the positive side of the second bolt on the negative side of the second bulb. So if you can understand what the's voltage readings should be, then after that we can learn what the wrong reading at any of these locations would mean. It would help you diagnose the circuit and lead you towards what type of fault it is and how you can pinpoint it. So spend a few minutes with this, and when you're done, just hit play, and it will advance to the answers in the next video 11. 11 Voltage At Worksheet 2 Bulb Series Circuit Switch Closed Answers Explained: all right, so let's go over the answers to this volt meter challenge. And remember, the purpose of this is so we understand what all the different voltage levels are supposed to be at the different points in the circuit because once you know that your diagnosis becomes much easier. And then once we go over a few examples of what the wrong readings mean, perhaps one wrong reading means that there's an open in the power circuit. Another wrong reading might mean there's high resistance. Another wrong reading might mean there's an open in the ground path. What we're doing is understanding what the circuit should look like. And then when we go to make a measurement on the car, or even when we're just trying to analyze the picture from the schematic and then comparing it to what already works on the car, we can get an idea of what's wrong with the circuit. And sometimes on some circuits on the car, you can almost diagnosis the whole thing just by going and seeing what works and what doesn't work. And comparing the schematic of a couple of circuits that perhaps share the same fuse or share the same ground. You can eliminate a good part of what could be wrong just by understanding what to look for . So as we go through the circuit, we're going to just identify before we put the answers up, we're gonna identify and put a number at the top of the red lead for each meter. What I want to know is if I have a 12 volt battery. If I was to put the red lead here and the black lead here, it would measure 12 volt. So now what I'm gonna do since I'm doing what we call voltage at measurements, I'm gonna leave my negative lead on the negative battery terminal and what all of these ground symbols are for all of these meters. It's just saying that the black lead of the meter is connecting to either the negative battery terminal or some metal on the car, which is connected then to the negative battery terminal through a wire. How much voltage would you expect to measure if there was 12 volts here? A. To the battery. If this wire was good, then wouldn't you expect that same 12 volts to be here? Of course you would So that's why I'll just put a 12 right here, indicating that that's what we expect to measure at this point. Now, if this fuses good, I should expect to measure 12 volts on the other side of the fuse. If I was to hook up my meter in this same fashion, So what about if the fuse was bad? If the fuse was bad, wouldn't I have 12 volts on this side? And then if the fuse was blown, wouldn't I have zero volts on this side? Because there would be a break in the fuse, which wouldn't allow the 12 volts to get to the other side. So that's actually how we look for and determine if there's an open circuit. We would make measurements along the power of path and find out where we no longer get the 12 volts that we should have based on the picture. So let's say that the fuses good here than I should easily have the same 12 volts on this side of the fuse that I did on this side of the fuse. So now we move our way up to the switch. Since this switches wired in series with the fuse and the switches shown closed. Now, I should also have 12 volts here on the input and 12 volts here on the output. Now, what about the circuit? What would it look like if the fuse? I mean, excuse me if the switch was open, so if the switch was open, wouldn't you still expect to see 12 volts on this side? If this whole part of the circuit was working and what would be the reading if the switch was open? Wouldn't you expect to see zero? Just as if it was like a blown fuse? If you were to measure on this circuit and you had a situation where the lights weren't working and you measured 12 volts over here and you measured zero volts over here, that means one of two things. It means either that the switch is open where nobody's activated it, or it means that the switches bed. So if the switch is actually activated and closed and not working, then there must be some type of break in the switch. Almost a ziff. The switch was open itself. But in this case, the switch is physically close. But it's still not working, and it's not getting any voltage to go past the switch context to transmit down the rest of the circuit. So if I don't see the 12 volts over here, that's telling me that the problem is the switch. But in this case, we have 12 volt. This is demonstrating a working circuit, so I expect to have the 12 volts on the output side of the switch, and the same thing would apply over here. Once we get to the input side of the first bulb or the positive side of the first bulb, I would expect to have 12 volts here because this wire is just allowing that voltage to reach that goal. Now, if there was an open somewhere in this circuit, what would I measure in the circuit? I would have all of the twelve's all the way up until that point. But when I came over here to measure and look for 12 on meter number five, then I would wind up seeing zero if there was an open or a break in this wire. So when you see 12 volts up to a certain point, and then all of a sudden it turns to zero where there is really no open circuit there. That's expected, then that is telling you that there's an open circuit in that area and you would actually have 12 volts all the way up. If there was a fault right here, you would have 12 volts all the way up to that point. And then as soon as you got to the other side of the break in the circuit, it would be zero volts, and there would actually be zero volts on every meter after that because it's a serious circuit and because it's an open in that power wire that is between the switch and the bolt . But now let's just continue on what the normal voltages are. I do expect to get 12 old at the positive or input side of the bulb, or the first bold and on the output side of the bulb or the negative side of the bulb. In this case, I expect to get six volts now. If this was the Onley bulb in the circuit and this other ball bowled, number two was not there, then this bulb would actually use up all the voltage because whenever you apply a voltage to a closed circuit, meaning a completed path. You're actually gonna use all of the voltage by the load or, in this case, the bulb in the circuit. But in a Serie circuit. When you put two or more bulbs in Siris, they actually share the voltage, and they share it based on the resistance of the different bulbs. But in this case, I have two bulbs that are the same type, so they're going to share it equally and split the voltage 50 50. So in this case, 50 50 comes out to six volt each. So if the first bulb has used up six volts, that means meter number six would say six volts, because the meter itself is just telling you the difference between where the two leads or touching. So if one lead is touching, where six volts is located and the ground side is zero volts than the meter is just going to say six folds and that's what it's showing over here. Six bolts and then, as we get to the second bulb, the six volts. Now that is on this wire. If this wire is good, we should see six bolts when we get to the other side of the wire, where the input to the bolt number two is. So I'm expecting to see six volt here. Now, what could be wrong if I see zero volts here, what would I have to do if I saw if I saw zero volts here? Let's say this is the first place I decided to measure. All right? We didn't make all these measurements along the way, and I decided the first place I'm gonna measure is right here. I would expect to see six volts if I understand the circuit because I know these two bulbs will share the 12 volts. But what could be wrong if I saw zero volts here? That could mean that we have some type of break in the circuit before now. If I had a break in the circuit ahead of anywhere in this point, if there was an open over here, I would see zero volts. By the time it got to hear if there was an open fuse or an open and this wire or an open switch, we're in opening this wire or even an open bold. The measurement here would be zero just telling me that the fault is back towards the power side of the circuit. So what I'd have to do is I'd have to go make another measurement back somewhere in this direction, to find out. Do I have 12 volts up to this point or the way they say the measurement is there 12 volts available at the input side of the switch? And if I wound up finding zero volts here, that would mean that the problem wasn't between here and here. It would mean that the problem getting zero volts here, I'd have to go further back towards the positive side of the battery to find out where, um, I actually losing the 12 volts. So anyway, just to finish up the readings on this particular worksheet, after you get through both of the loads or in this case, all of the bulbs at the end, you're going to use up all the voltage to the reading on meter number eight should be zero volts. And if you were to put a volt meter anywhere the red lead anywhere along this wire on the way back, you would also read zero volts and that would be normal, but let's talk for a minute. About what would not be normal. What could be wrong if I measured 12 olds right over here, where I'm expecting zero volts. If I measured 12 volts at this location, that means that this bulb is not using up the 12 volts. This bulb is not using up to 12 volts, but if you think about it when we had an open switch, didn't we have 12 volts on one side and then zero volts on the other? Wouldn't it be the same thing if I had an open in the wire going between the battery and the and the ground side of the second bulb? So let's say that there was an open right here. Since there's no complete path in the circuit, the bulbs air not gonna use up any of the voltage because there's no complete path back to the battery. Without the complete bath, there is no current flow. And then there's no voltage used up. So think about it. Wouldn't I have 12 volts moving down this wire? Past the switch up to the first bowl would be 12 volts. And if there is no ground where there's an open in the ground. I would actually measure 12 volts here. I would measure 12 volts here, and I would even measure 12 holes here. So when you get a situation like that, what it's doing is it's telling you that 12 will reading where you expected zero here or where you expected six. Here it means getting 12 in these locations is saying that there's no ground path or something after that has an open in it. So then you would just have to move forward to find out where the open is. And if there were places to check along the way, let's say there was a place to check here if you had 12 volts here and then there was a place to check here and you had zero. That would mean that the open was in between those two points and the same thing. What if what if there was an open in this bulb? What we would wind up measuring is 12 volts on this side, and then we would measure zero volts on that side because the 12 volts has a complete path up to the input or positive side of the first bulb. But because the bulb is blown like an open fuse or an open circuit, there is no complete path back to the battery. So, just like you would have the 12 and zero here when the switch is open or if it's defective , you would have the same kind of readings a 12 here and a zero here, meaning that the bulb is blown. So just review these answers. Here I have 12 volts for meters one through five, because that's what I expect to measure 12 all the way along the path. And then I expect six volts after the first bulb because that first bulbs going to use up half the voltage or six bolts and then the second bowl will use up the other six volts. So that's why meter number seven is actually showing six volts, just showing that the six volts after the first bulb has now moved toward the other bulb and is available at for that bulb as well. And then the second bold uses up the rest of the voltage. And remember the voltage on. Lee gets used up if there's a complete path. So if there's an open in any part of the circuit. Then the whole circuit is dead, similar to when you have a set of cheap Christmas lights and one bulb goes out and the whole circuit goes down. So I hope this explanation helps. What we're gonna do is we're gonna examine a few circuits that are similar, perhaps a serious circuit and some parallel circuits, and then we'll apply them to some more complex circuits. If you can understand what you expect him measure, then knowing what the wrong answer means, your diagnosis becomes much simpler. And the hardest part in most cases when you're working on a vehicle is to find the access point that's easiest to get to. That will give you the most information. When I'm moving along in the diagnostic process, I do not have to make a check here and here and here and here and here and here to see if there's 12 volts. Couldn't I just come over to the easiest access point? What if, where the bulb is was easier to access than the switch now, Oftentimes the fuses an easy place to access, so if you could easily access the fuse by all means see if there's 12 volts on each side of the fuse. But remember, connect your meter lead where the negative lead is connected to the metal on the car or to ground, and then the positive lead goes first to the one side of the fuse and then to the other side of the fuse. So in diagnosis, what you're trying to do is diagnose the whole circuit in the least number of moves or steps that it's possible to take. So if I come over here and I expect to get 12 and I get 12 it's telling me that this whole part going all the way back is okay. And couldn't I then come over here and see either if their six year or I could come here and see if there's zero here? But if the bulbs aren't lit when I'm checking it, I would probably be better off checking here or here. And since I were ready, made my first test on this side of the bulb. If I had 12 here, I would possibly want to check right there on the other side of the socket, and this would this test would be while the bulb is actually plugged in. And when you're doing a test, would a volt meter when the bulb is plugged in? What we call that is back probing where we have the circuit actually hooked up where we didn't remove the bulb to test for the voltage there were probing it to see if that voltage is being used up by the first bolt. Now, if the circuits dead and the bulb was bad, then I would have 12 volts here, and I would have zero here if the circuits dead and perhaps the second bulb was bad. The reading that I would get on this side of the first bowl would actually be 12 because the second ball being bad would mean there's no complete path, so the first ball wouldn't use up the voltage If there's no complete path. If this gets a little bit confusing the first time you hear it, it's no big deal. What we're gonna do is we're gonna go over several examples so that we can explain it a few times where it starts to sink in, and then we'll try to do some examples where I put the wrong readings down and see if you can decide what could be wrong, what type of fault is present and where the where the fault might be. So I hope this helps for now, and we'll move on to the next circuit in the next video. 12. 12 Voltage At Worksheet 2 Bulb Parallel Circuit Switch Closed: here is another volt meter worksheet to test your knowledge, see how you are understanding the volt meter and what the readings should be when they're expected at certain areas of the circuit. So just like we did in the Serie circuit, here's a parallel example where we have two bulbs in parallel. I have two separate paths here and I have eight meters again and we're doing voltage at measurements, which just means that the negative lead of all of these volt meters is connected to ground the negative battery terminal or metal on the car. And then the positive lead is being connected to a point in the circuit. So we call that voltage at measuring. Number three is measuring the voltage at the input side of the switch meter. Number seven is measuring the voltage at the positive side of the second bulk. So what I want you to do is try and figure out what you think the expected value should be . And once you understand what the's normal readings are, getting, a reading that is not normal will help you decide which direction the fault is from the point you're measuring and what type of fault it is. So give it a try and we'll go over the answers in the next video 13. 13 Voltage At Worksheet 2 Bulb Parallel Circuit Switch Closed Answers Explained: just like we did with the Siri circuit worksheet. What we're gonna do is go over the answers in the same fashion where we want to follow the 12 volts along the path and get an idea of what would be the voltage level and what would be the normal level at each of these points in the circuit. And once you can figure out what those levels would be, your well, on your way of knowing which way to go, which direction to go after you make a measurement or what's wrong with the circuit or what type of fault you have and how to go about narrowing it down even further. So in this picture, once again, we have the circuit itself, which is just this drawing here around the outside. This is one path, and a parallel circuit is really made up of a couple circuits put together where they're sharing the power and the ground where the power or the ground. In this case, I have to separate paths and they split here and they come back together here and remember , the purpose of a parallel circuit is so that we can have 12 volts applied to each branch of the circuit. So I have two branches. I have branch number one over here, and I have branch number two over here. If I was to measure 12 volts, if I was to put my volt meter between these two points, the positive battery and the negative battery, that makes sense that you would have 12 volts. And remember once again that when the volt meter this is just drawing the negative lead of the meter as if it's connected to the metal on the car or the negative battery terminal. So all of these points where I'm placing my meter, you wouldn't be using eight different meters. I'm just doing it for the illustration. It would be the one meter that you would move to any of these locations to decide what the measurement is when you actually make the measurement. And most of the time we don't make all of these measurements. We pick a spot somewhere in the middle of the circuit, which is easy to access. Perhaps it would be this location after the switch. Perhaps it would be on the power side of one of the bulbs because if I was to get the voltage that I was looking for at this location. That would tell me that the area going back the other way is good and that my diagnosis would be moving forward. And there's also diagnosis that you conduce you based on what part of the circuit is working. So let's say that one bulb was working and the other bulb was not working. Couldn't you then reason out that if bolt number one was working, wouldn't it be absolutely true that all of this part of the circuit that's highlighted right now has to be good and that your fault has toe lie in this area over here? What you can do is you can narrow down where you would need to check on the car just by understanding what works and what doesn't work and trying to narrow it down on the schematic before you get to the car. Usually, you would go to the car first to verify what the fault is and make sure you actually have that condition. But then I would go to the schematic. I would spend more of my time making sure I understand the picture. And where is the easiest place to measure that I would taking things apart that later on you find out you didn't need to touch. So if I was to measure at this positive side of the fuse, then if I have 12 volts here, it would be easy to understand by now that we should have 12 votes here. Unless there's a fault in this wire and the same thing on the other side of the fuse. If the fuses good, I should read 12. If the fuses not good, I would wind up reading zero. But what if I was to read zero here as my first measurement? Does that mean that the fuses bad? Well, let's think about that for a second. What would be wrong if I actually had a zero here and zero here? Is that the fuses fault? Or is that the fault of this wire before the fuse? If you make your first measurement after the fuse here and you get zero, that doesn't automatically mean the fuses bad, because it takes two measurements to decide on the fuse. If you're doing it in this fashion, voltage at you would expect. And let's just get back to what we expect and we'll go more into the diagnosis. I'm always leading towards teaching something about what does it mean and what is the diagnosis? Where does it take you? But let's finish with what the normal readings are, and then before I get carried away, will continue with some more diagnostic skills. It's easy to see that all of these locations on the way should be 12 volts. If the switches close, there should be 12 volts on the output side of the switch. And because there is a path that's not broken all the way up to the positive side of both bulbs, it's easy to see that there should also be a 12 here, and there should also be a 12 here and then, since this is the only bulb in the path and remember, this is one path which acts like it's it's own Siri's circuit, and this bulb would then get the full 12 of that series circuit. So if it's going to use up the full 12 the reading that I'm gonna have after the bulb is zero and the same thing on this side. I have 12 volts on the positive side, of the bulb and after the bulb, I'm expecting a zero. So if we went over our readings, the volt meters one through four should all be 12 volts as well as meter number five and meter number seven. Because there's 12 volts available, we would expect there to be 12 volts available all the way up to both of the bulbs and then on the ground side of each bulb. If the bulb is functioning in the circuits functioning correctly, I would expect to measure zero because each bulb in each path will wind up using all of that 12 volts, respectively. So I should measure 12 volts on meter five but zero on meter, six, 12 volts on meter seven and zero on meter eight. What would be wrong if I had 12 volts on meter number six? Let's say that the first place I measured was meter five and I had 12 volts. And the Onley fault is that bold number one is not working. So I go over to this location and I use meter number five or I hook up my meter in this location and I measured 12 volts, so that would tell me that the problem has to be down either the bulb or the wire after the bowl. So if bold number two is lit, it would be easy to see that all of this wiring going all the way around has to be good. And once I get the 12 will reading over here, I can now also highlight this as being good up to the ball because I have 12 volts up to the bolt. So remember where a detective we're trying to eliminate all of the things that are good and then what we have left is the fault. And do we have an answer yet? Do we know what's wrong? Would you think it's the bulb? Is that the only possibility? Actually, we need to make one more test if we have the possibility of the bulb being bad. But we also have the possibility left that it's in this wire. And when I move my meter, two meter number six or location number six, what reading would mean that it's the bowl? And what reading would mean that it's the wire? Now, remember, if I have 12 volt on the positive side of the bowl and zero volts on the negative side of the bulb, and the bulb is lit that is normal. But if I have 12 volts on the positive side of the bulb and zero volts on the negative side of the bulb and the bulb is not lit, those readings are telling you that that's a bad bowl. And if I was to get a 12 over here on meter number six instead of the zero that I expected , that would mean that the bulb is good, allowing the 12 volts to go through it. But it's not using it up because there's no ground path. And then because I have bold number two that's working. And because I know the ground pet from this location, back to the battery is good. Otherwise, bold Number two would also be bad. That means that this 12 vote reading here would mean that this wire between here and here is broken, so we'll get more into this diagnosis method of where you highlight the part of the circuit that is good, leaving you to then on. Lee have to test the part that you still haven't proven. If it's good or bad yet, and we'll get into more complex schematics, and the more complex schematic, the more you will find that this method will be a lifesaver toward your diagnosis. Because when you understand what the reading should be and can confidently eliminate sections of the circuit at a time before you even go over to the car, you will be amazed at how quickly and how much time you save on diagnosing. And then the repair part is usually the easier part. In an electrical diagnosis, Diagnosis part usually takes longer, and the repair of replacing the bulb is usually something that's relatively quick on occasion. Finding the location of an exact break in the wire could take a little while, depending on if it's a wire that goes from the front of the car to the back of the car. And if that was the case, you would actually look for some type of connectors located between the negative side of the bulb and this junction point here. And if there are connectors in the harness somewhere, then you would go to that location and perhaps make a test midway. But on this schematic, there are no connectors shown, so that means the fault would be somewhere between here and here, and I could then find where this junction point is and run a new wire from here to here. Or I can try and isolate the fault by examining if that wire looks like there's an area of damage. If I can see the area where the harnesses running, we'll move into diagnosis of a more complex circuit in an upcoming video. And for now, I hope you understand the readings that you expect to get on a basic Siri's any basic parallel circuit, so that we can then apply that to something more complex but still use the same thought process and the same method of highlighting what's good and leaving us with what we still need to check or prove, So I'll see you in the next video. 14. 14 Series Schematic Variations: Wouldn't it be great if every manufacturer used the same symbols for all of their switches and fuses and bulbs and the battery symbol? Wouldn't it be great if everybody drew their pictures the same way? Alright, let's stop dreaming for a second. Every manufacturer could do whatever they want, and every program that makes schematics for the different manufacturers may use different symbols or variations of the same schematic, but electrically, they're still the same. So what I've done here is I've put four different schematics on this page and therefore variations of the same Siri's schematic. Now we've seen this schematic here before in the top left, and it's just a simple Siri circuit with two bulbs in it, and the other three pictures are all exactly the same. Electrically, they're just drawn differently. So when you pick up a schematic from a manufacturer, some manufacturers will label the components right on the page right on the schematic for you and others will give you some type of glossary or key or an area of their schematic program, where you can view a few pages of information to tell you what they're different symbols mean and then on the schematic themselves. They don't label everything, so you just have to get used to the different companies that are out there. That makes schematics and the different manuals that the factory make, because the schematics can be different but electrically, the similarities air still there. So once you get used to a few of them and get some schematics under your belt, where you're comfortable with some of them, you'll start to find out that you can almost recognize what the different symbols mean just from your experience working with them now, one other point to mention whenever you're looking at a schematic. Usually in most cases, it's drawn where any switch or device is in its normal position, as if you were not pressing any switches or buttons. So in this series circuit, where the two bulbs could be lit up if the switch was closed. Since this switch is operated by the operator and is normally in the open position, then it would be drawn on the schematic in the open position. And then, if you wanted to try and figure out what the voltage readings would be if it was open or closed, you could then just draw a line across here to try and figure out what your readings, maybe, or just realize that you're doing it. With the switch closed, I would always take my pan on a piece of paper. I usually print the schematics and draw right on them. A couple of words about the ground. Simple Here. It's rare that any manufacturer will draw a picture that shows the complete path going all the way around back to the battery, some schematics that are on the battery itself or the alternator and charging system. Sometimes they'll have the battery in the schematic, where they show the ground path going all the way back to the battery. But most cases you will see something that looks more like this one on the bottom, where they just put a ground symbol connected to the negative battery terminal and a ground symbol connected to any other part of the circuit that is also connected to ground. So regardless of how far down this wire went before they drew the ground symbol, or if they made a turn and then came down further and then drew the ground symbol, it all means the same thing If you see two ground symbols on the page, it means they're connected or they're supposed to be connected because they're both touching either metal the frame of the car, and they're both a connection back to the battery through the ground path. Even if there was 3456 or more ground symbols on the page of that schematic you're looking at, they are all electrically connected. Or at least they're supposed to be. Then when you come over here, I have a couple of pictures. Some manufacturers will draw their battery at the top of the page, and they won't draw a battery symbol. They'll just right B plus. So they made sure a little bubble box here and put B plus in it, and then they'll draw everything from top to bottom. Now they could also draw it from bottom to top if they want. I've seen a couple that go from bottom to top, but most cases I've seen there they'll be from top to bottom, and this picture right here electrically is the same as these other two pictures over here that we were just speaking up and another thought is they can draw it in any pattern they want. It doesn't have to be a straight line, although electrically, it still is the same picture. So some companies, if they need to put a small picture or some information over here on the page, they may draw the schematic so that it looks like it's going around that picture or other information that they're providing. But it's the same picture as if they were drawing a straight line. Electrically, it's the same circuit and one last thing to note the length of the wire in the schematic. For example, the wire between the fuse and the switch is drawn shorter than the wire between the two bulbs and the wire between the bulb and the ground. The length on the schematic has nothing to do with the length of the wire on the car. This wire between the fuse and the switch could be 10 feet long, going from wherever the fuse boxes located to wherever the switch is located and the wire between the two bulbs. If they were in the same lens, they could be right next to each other, and the length of this wire means nothing. So all all you get from the schematic? Is that where the electrical connections are? And what is the flow of the path of the electricity when the circuits on, That's what you're using fear diagnostic in your analysis. So the length of the wire on the diagram has no effect on what the real length is. 15. 15 Schematic Wiring Differences: we're gonna be working with this schematic in an upcoming video, but I wanted to point out something about the way the wiring is drawn on different schematics from different manufacturers. Sometimes you'll see there's a dot like you can see here, where the wires air crossing each other or connected to each other, and sometimes they put a dot, and that means they're connected. But sometimes they'll also do this. They'll just cross the wires without the dot, and that could also mean they're connected. When they use the DOT, it almost always means they're connected. And when they use this symbol down here, where they look like they're bypassing the wire, the little curved part of the wire as it goes past the other wire, that means they're not touching or not connected or they shouldn't be connected. But when you see it drawn with no dot and with no bypass looking hook there, what that could be is some schematics will draw where this picture means they're not touching, and this picture of year means they are connected, and other schematics will draw the picture as if this means they are touching. And this means they're not connected. And then there'll be 1/3 group where they'll use this meaning they're connected, and this meaning they're not connected. So you might see any of the three possibilities. But just realize that this one just about always will mean connected, and this one just about always will mean not connected. But it's this middle one that could be either depending on the company that's using it. But you can usually tell from just looking at the diagram. And if you can't, you would have to look at the resource material that comes with the schematic or the schematic symbols page that the manufacturer usually provides that describes what their symbols mean on their schematics. 16. 16 Brake and Park Lamp Circuit: Let's get a little bit more complex. Now On this schematic, we have two fuses on the same schematic 20 amp fuse. That's for the brake lights and a 10 AMP fuse. That's for the park lights. We have two switches. This one's a push button types, which and the park lamps, which is a physical switch that you turn on and leave on or turn off and leave off. And then we have the four bulbs. Notice we have the left right clamp and the right break lamp on this side of the page and the left part clamp and the right park lamp on this side of the page, and we have two different grounds. There's a ground over here and another ground over here and noticed that the left side break land and the left side park clamp. Use this ground and the right side break lamp and the right side park land used this ground . So now that we understand what the circuit has to offer, let's move on to the next video, where we actually do some diagnosis 17. 17 Brake and Park Lamp Fault 1: we have our brake light and park light schematic, and we have a condition where both park lamps are inoperative. We're going to narrow down the possibilities. Remember, we're a detective. When we're diagnosing an automotive electrical problem, we're eliminating everything that we know is good and then leaving what we have to check as the few things left. And sometimes you can eliminate an awful lot of the circuit just by understanding what works and what doesn't work. So both part clamps in up. We have the brake lamps where it will step on the brake and you'll see that the brake lamps do work. If both brake lamps work, then we can highlight a part of the circuit that the brake lamps used. Now notice here, 12 volts comes through the 20 AMP fuse. It gets to this point, and it does split to go toward the park lamp side. But it also goes to the brake lamps. And if the brake lamps work, then this switch must be good and this bold must be good. And this wire must be good and this ground must be good. And then where we left off at the split, a moment ago. It also must be good from here, through the left break lamp bulb and all the way down here. And also this ground must be good. So where does that leave us? It leaves us with the to park lamp bulbs, which could still be bad, and the wiring in those particular circuits. That could be bad. And then it also leaves the switch and the wiring by the switch and the fuse and the wiring by the fuse. Now, in most cases, and I would say almost all cases unless someone else has worked on the car, there will only be one fault. Most of the time when there's two faults or three faults in the same circuit, there's one original fault, and then a couple things left disconnected or broken from the person that was checking it, that wasn't able to find what was wrong. Initially, when you're doing your diagnosis, you could eliminate things that could suggest that there had to be two faults and attacked the problem as if it has to be one. And then if for some reason one of the test you make proves that there has to be more than one fault, Then by all means, you would go to looking for two individual faults and you'll be almost there to the answer . Anyway, the reason I bring this up is if we're only looking for one fault that could cause both park clamps Stand up. We could also eliminate this wire here and the bulb and this wiring and the same on this side. We could eliminate the left side park lamp wiring and the bold and this wire after the bulb . So that would mean that our fault needs to be between this junction point all the way back to here and over to this junction point. So just by understanding what are condition is both park lamps and operative and finding out that the brake lights were we have narrowed this down to where all of our testing is. Either in this fuse or switch and the related wiring. We would only need to come over perhaps to the fuse, because it's probably the easiest to get to and check for 12 olds here and 12 volts here and then if we had that, we can come over to the park lamp switch and check for 12 year. And then we should also have 12 volts on the output side of the park lamp switch. And if we didn't but had the 12 volts on the input side and we were closing the switch and we still had zero here, that would mean that the park lamps, which is bad and the same thing if it was the wire. What if we had 12 volts here at the output of the park lamps, which But when we got down here, we measured zero. Wouldn't that then mean that the wire in between these two points were bad? For the purposes of this video, let's say that the fault that we have on this car is actually located between this junction point and the power side of the fuse. So let's make believe that there was an open here. And if that was the case, how many actual diagnostic tests would have been necessary to diagnosis this once? We've eliminated all of the things we've already spoken about. That have to be good. You would make your first test, perhaps at the fuse or the park lamp. But if you chose the fuse and you came over here and looked for 12 volts at this location and look for 12 volts at this location, you would have found that you had a zero and a zero right away. You would have had the answer that the fault has to be between the power side of the fuse and this junction point, because there has to be 12 volts at this junction point because it's the same 12 volts that's allowing the brake lights to work. So your fault had to be between the junction point and the power side of the fuse. In the next couple videos, we're gonna go over using the same schematic will demonstrate how, by highlighting the parts that are good, we can narrow down so much of the circuit in so many cases that the amount of testing that we need to do on the car, or even if you're having someone else do the work for you. The amount of components that could be bad or wiring areas that could be bad will be very small, and you'll be able to focus on those areas where, if somebody told you that a problem was in the grounds and they had to run all new wiring because the ground was bad. You would know that that wasn't correct, because your fault in this case had to be between this point right here and this point right here. So let's move on to the next video and tackle the next fall. 18. 18 Brake and Park Lamp Fault 2: in this example, we have a condition where the left break lab is inoperative and the left park lamp is inoperative. And once we verify that, that is actually the case on the car. If we come over to the schematic and highlight the parts that have to be good, you will find that sometimes doing this will save you so much diagnostic work and taking things apart on the car will not be your first choice anymore. So if the left break lamp and the left park lamp are inoperative but the right break lamp and the right park land both work, I can highlight that the path through the brakes, which has to be good and the path through the right break lamp bulb has to be good over to this ground has to be good. And the same thing goes for the Parkland. If I was to come this direction through this fuse through the park lamps which and through the right park lamp, that also has to be good and the same ground is used here. So now that leaves us with the path from here to here and the path from here over to here now remember, before we spoke about how most of the time the condition is caused by one fall unless somebody's already worked on the car, and perhaps they've created a second or third fault. So if it's only one fault causing both of these problems, wouldn't it be true that if there was an open in the wire here, causing this left break lamp, not toe work, that wouldn't affect this left par clamp? This left park lamp would still be good. And if we had a fault where the left park lamp bulb was blown where there was a fault in this wire before the left park land with that effect the wiring and the bulb for the left break lamp and the answer is no, it wouldn't if the problem is the bulb and it was two things wrong. It would have to be two bulbs that are bad or two breaks in the wire, one on this path and went on that path just by narrowing down and highlighting the stuff that has to be good and then reasoning out that if we're looking for only one fault that could create both of these conditions, we would narrow it down toe, where the fault has to be between this junction point and this ground, and this is without doing any tests on the car, other than to verify what works. So as we do more and more of these, you will see that sometimes you can narrow down so much of the circuit without having to make any tests on the car. And then maybe you make a test or two to narrow down the last part or the last step of the diagnosis. It doesn't always work that way. Often times you will have to make two or three tests because the condition may not eliminate too much of the circuit. But there are many, many cases where most of your diagnosis is done right on the piece of paper with a highlighter. So if you have the ability to print out the schematic you're working on, I recommend it because I had a few different color highlighters in my toolbox, and I would spend a few minutes highlighting a schematic and then walk over to the car and know exactly where to test to eliminate the last potential possible cause. 19. 19 Horn Schematic Circuit Explained: This is a horn schematic from a General Motors vehicle, which uses a relate to control the horns. And a relay is a device that allows a low current path in the circuit. So this would be the low current path here, the really coil, and in this case we have two different ways of turning it on. We can use either the horn switch or the body control module, or BCM can turn on the horn relay as well from a signal from the theft deterrent module. And that kind of information about the circuit and the way it operates there is usually in the manufacturer's manuals. There is a section called Description and Operation, which on occasion it could be part of the schematic, where they describe how it operates. But most of the time it's in a separate section where you find this description and Operation page, and it will describe how that particular circuit work so it might say something in words. Power is supplied through a 10 AM views to the relay coil of the horn relay, and a ground path is supplied by either pressing the horn switch or through the BCM relate control when it gets a signal from the theft deterrent module. And then when the Reedley is activated, it closes thes switch inside the horn relay and allows the 20 AMP circuit to power up the horn. And in this case, we have a dual horn assembly, so description operation is there for when you need further clarification, where you can understand the picture just from the way it's laid out. Now on this picture, you pretty much can understand most of what's going on. Maybe you wouldn't know when the BCM would be using this horn control circuit, but with the description and operation they're telling you, it turns on when the theft deterrent module sends a signal to the BCM, or when you're hitting the panic button on your remote control for the car to outline the two pats for power load and ground. Let's just take a quick look and highlight thes two pads. The power side of the circuit would be everything up from where the 12 volts is supplied all the way to the relay coil, and the relay coil itself is the load here. This is the part that's going to use up the voltage and remember relays gun electromagnet Like when you were in school science class. When you were younger and you took a piece of wire and wrapped it around a metal nail, it would become an electro magnet. And inside a relay, they've just taken very thin wire and wrapped it thousands of times around a piece of metal core that becomes the electromagnet. Just like the experiment you didn't school. That's what will pull this switch over when we give power and ground to the wire that is connected to the nail, which in this case, is the relay coil instead of a nail. The ground path would be then everything from the bottom of the really coil all the way to the ground. And like I said before in this case, either switch could be the ground for this. So I could either press the horn switch and I would have my ground path through here. Or if I hit the panic button on my remote, the BCM would get the signal from the theft of terror module, and it would close this, which and that would give me the completion of the ground path in this direction over here . Now let's look at the power load and ground on the switch side of the relay. We would have the power side would be everything from where it's 12 volts up until and now this which would be closed when the relays activated. And the power side would be all the way through the relay switch and up to the positive side of the horn assembly itself, where inside the 12 volts would actually be available all the way up to where the horn coil starts on each horn. And then the load would be the horns themselves. And then the ground path would be this area underneath. And in this case, the horns. Aaron parallel. So they both get 12 volts so that they can sound nice and loud. And this ground path is shared by both horns down to here. So that's the basic operation of the circuit. What I'm going to show you in the next video is some of the additional detail that gets put on a schematic that can be very helpful for where certain connector locations might be, what they look like, the different components that are involved, like you might see the BCM identified a little differently on the picture, you might see the location of where these fuse boxes are. So in the next video, I'll show you a more complex version of this schematic, how you would see it from the factory and we'll go over what all those different other items are so that you'll understand them. 20. 20 Horn Schematic Additional Schematic Details: here is the same schematic we had before. You can see the same power load and ground through the relay coil and down through either the horn switch or through the horn relate control of the BCM. And then we have the switch side again through the release switch and down through the two horns and to the same ground. Now, on this page you're seeing a lot more detail and a lot more features, which I'm going to describe what they mean because many manufacturers use similar ways of explaining what certain things and certain functions are. And after you get used to reading several schematics from different manufacturers and what their meanings are, you'll be able to pick up a schematic, and sometimes you'll need to reference their material. But ideally, if this is for your car and you're doing it as a do it yourself project, then you'll get familiar with the company that makes the schematics for your car, and you'll become very proficient at what most of the symbols mean and what the items on the page are just by looking at it without referring to the other reference material. So let me explain what we have here at the top here of it, says Fuse Box under Hood. And we're actually showing you this illustration, this dashed line that goes all the way around here and that's actually showing you the fuse box. And what it's saying is that this views and this fuse and the relay itself are located in the fuse box that's under the hood. This core happens toe have a fuse box that's in the dash on the left side of the dish, and it has one on the right side of the dash, and it also has one under the hood. But this schematic for the horn on Lee requires the information for the under hood fuse box . So that's all they're showing here. Notice that there's also the line around here that is designated to be the fuse box is a dash line and noticed that it's a solid line being used for the relate, and it's a solid line being used for the horn assembly. The BCM down here is also a dashed line, and what some manufacturers will do is they'll use a dash line and all it means is we are showing you on Lee some of the wiring for the under heard fuse box in this picture. So that means that there's more wires than just this one and this one and this, these other two down here, the fuse box has a lot of wires. So the dash box just means that we're not showing you all the electrical connections and wires. And for the BCM, the same thing is true. We're only showing you the one wire to the BCM. That is the ground for the one really control. We're not showing you any of the other wires, and there are many wires for the BCM. So the dash box just means that we're only showing you some of the wiring for this particular cars BCM wire. Yet for the horn, we're showing you the two wires. Those are the only two wires that go to the horn. And for the relay, there is actually four terminals inside the fuse box going to this, really? And since they're showing you all of them, the relay actually has a solid wiring box around it. Now, inside this area, notice it says connector I D. And this is showing you c one through C seven, which means that there are seven connectors connected to this fuse box, and then they're further describing them how maney terminals air in each connector and this 68 means that there's quite a few terminals, and in this case it's a square block of terminals where it could be two rows or it could be four rows. Whatever they're doing, they're adding up to 68 total terminals, and they're making the rose in a fashion that comes up to that. So it could be two long strips where it could be a block form. And in this case, it's a block form where there's actually a bolt going through the middle that holds it to the fuse box itself to maintain the connection. And the number 68 doesn't mean that there's 68 wires going to it. It just means that there's 68 terminals and some or all of those could be used. And then the molded body of the plastic connector itself is light grey for connector. See one. So if you needed toe, identify a certain wire or terminal and notice down here while we're talking about that, where the wire for the horn ground comes out of the fuse box. It comes out of connector. See to Terminal C 12. So if you needed to find that wire, there are seven connectors, but connectors C two is one of the larger connectors is actually three large connectors, but you would identify it by the black connector and then, if you needed further illustration to find that exact wire cause sometimes you do, because you need to know the reference points of where connector C two is. And then which of these terminals is Terminal C 12? So there's another area of the manual where you can actually see a picture of the connector body itself, and they will label the different terminals so that you'll know which one to do your test at and make sure that that wire is good there. That's necessary. Notice also that the BCM is giving you the connector information. There are great connectors. One of them is only 16 terminals, one as 24. And then there's one pink connector, which is the same size as the gray one, also with 24 and the Onley wire. That's for the horn here is in connectors. See one terminal a six. So that would be the great connector that has 16 terminals that you would need to disconnect if you wanted to run a test on this particular wire. So let's go to some other things that are on this picture. Notice. Over here we have these donut looking things, and it's labeled P 200 then they have a tiny dash line going across here. What this is saying is, First of all, this donut looking thing is called a pass through, and this is where the wiring is actually passing through an area of the car that's metal. And in this case, it's the firewall. There's actually an area of the shop manual for this manufacturer that tells you that if they use 200 as their number or to a one or the number is in the two hundreds than that wiring is located in the engine compartment. And if they used the number 100 then it's located in the front, near the radiator in the headlights, where that where that wiring would be. And this little dashed line here is just showing that the P 200 is for both of these? All they're doing is saying P 200 they could've ropey 200 over here a second time, but instead they wrote p 201 time and put this small dashed line here, meaning that both of these passthroughs R p 200. So both of these wires are going through the same passed through. There's actually not too. There's only one, but the way they wanted to spread out the wiring, they're showing you that both of these wires are going through the same passed through P 200 on the car. What else do we have here? Up here? We have an area where you see that the power that's being supplied to the horn relay coil does go through this 10 AM fuse. But before it gets to the fuse that actually splits off and go somewhere else in the fuse box. Now they're showing you this just to show you that this area does feed another part of the fuse box. They don't give you the extra detail on this picture, but they are showing you where you could find that extra detail if you wanted it. There is a schematic called the Power distribution schematic for this manufacturer. And if you went to that Siris of schematics, you would find the detail of where this goes. And what it's gonna be doing is it's going to be going to an area where maybe there are several other fuses branching off of this same power wire here, where it feeds multiple fuses. And then, if you were looking at the power distribution schematic, going back this way towards what they would have would be like a maxi size or a large refuse, perhaps a 40 amp fuse protecting this whole circuit. And then they break it down into lower and fuses for the individual circuits themselves. So that's what they'll sometimes do. They'll use a large views and then have several smaller fuses running underneath it. But the schematic diagram right here is just showing you the parts that are needed for you to understand the horn circuit. But they are showing you that there are other things that air on this picture, that if you needed them, you could find them and where you could find them and the same thing down here for ground distribution. This ground, which is labelled G 101 and notice. I have a spice pack here. SP 101 The Spice Pack is actually being represented by this dash box. And remember, the dash box means that there are more wires than were actually showing, So they're only showing terminal EMS wire coming into this place pack. But this place pack actually has a number of wires, and the exact number doesn't matter. But if they're using a letter N, it means there's quite a few cause they'll usually start with Letter A and go through the alphabet. This manufacturer decides to skip certain letters like, Oh, because it's sometimes confusing with Q Will they'll skip certain letters? But they'll give you that information, like I said in the shop manual, where they give you the details of how their schematics are interpreted. So this ground distribution is showing that there are several other wires coming into this block where all of them then get connected together. And then that block itself is grounded, meaning that this ground is used for more than just the horn circuit. The reason that this information could be valuable is what if the headlights use this same ground and if the headlights were working, then you would know that this ground from here over to this point and down to here was good . And if the ground part of the horn circuit was bad, it would have to be from this spice pack up through to the horns themselves. So having that additional information, sometimes it could save some time where you could just test by referencing what else is on this schematic. And the way you find that you go to the ground distribution schematics just like power distribution schematic. And it would show you the breakdown of all of the wires that are entering into this this ground distribution center so that you can see what else is on that that is being grounded . Agee 101 The other thing that I just wanted to mention. We've already talked about connector see to Terminal C 12 and noticed that here it's terminal M of this spice pack, which is the wire coming from the horn and then notice We have letters A and B on the horn assembly itself. So this would be a two terminal connector and one would be labeled terminal. A one would be labeled Terminal B. Many manufacturers will also put the color written on the page. They might label this wire green, and this wire might be labeled black. Or sometimes they'll just put the terminals on. But either way, you get used to whatever the manufacturer is that your using. And as soon as you do some repetition with their schematics, you start to get comfortable with it. And then, once you've done a group of schematics with one manufacturer, you go over to another manufacturer to check. Then perhaps you have another car that you want to look at, and you'll find that many things air similar. You'll find some things that are different. But again, once you look at a few different schematics from that new car that you just bought or your second corps, then you'll become familiar enough where it's almost second nature, where you'll pick up a schematic and you'll be able to recognize the different things on that page. And again, if you need to help you, just go to the reference areas in the manual or online and try and find the information that you need. We also have the connector actually being drawn here where it's showing you the actual terminals that air inside the connector, and these are actually trying to identify which one would be the male side of the connector and which would be the female side of the connector. And the one that is actually protruding out is the male side of the connector, and the one that is that looks a little bit more like a receptacle is the female side of the connector. So go figure how they have they bring that into play here on an electrical schematic. But it was always fun talking about that to the class because they get a laugh out of it. That cover is pretty much what's on the schematic and all the different things that you can find as extra information on the schematic that you'll sometimes find. It's not always there. Some manufacturers don't put all of this information there. This will give you a a very good head start into getting used to the different terminology and the different features that you'll start to find on different schematics. As you look at them as we move forward in the next couple videos, what we're gonna do is simulate a couple of faults like we did on the lighting circuit, and we'll see if we can diagnose the fault and limit or narrow down the number of tests we might have to make on the car and in some cases will even be able to narrow down, eliminating a good chunk of the circuit just by understanding how the circuit works. So when we get to the next video, you'll see how that becomes very important. 21. 21 Horn Schematic My Horn Sounds Like a Sick Cow: in this video, we're gonna be diagnosing a horn problem where the horn doesn't sound right now. Many people, If the horn didn't sound right, they would just go out and buy a new horn and put it in. And if it was the horn that was causing the problem, they'd be happy and say, Hey, I diagnosed and fixed my own car. But there really wasn't much diagnosis there. That was just parts replacement. And if they happen to be right, they look like a hero. And if they happen to be wrong, then they chalk it up to experience and say, Well, it must be something else. This must be a really difficult problem. But the truth is there is a way to narrow it down and diagnosis to figure out what you need before you go out and buy the part in this case, because the horn doesn't work right. But at least it's working. That's gonna tell us that this whole side of the circuit here on the relay coil side has to be working. It means that the horn switches working and all the wiring from the relay to the horn switch has to be good as well, as well as the power supply side of the horn relay coil. We call this the control side of the circuit because it's the side that actually operates the other side of the circuit, which is called the switch site. In this case, decide that the relay switches in would be the switch side. That's the side that actually powers up the warn. And if you remember, the job of the relay was to allow this lower current circuit the control side to control a higher current path, which is the switch side of the relay. So just by having the horn operate at all, we knew that the control side was good. But now we have to test the switch site, and where you start in the circuit doesn't exactly matter. You could start up here a the fuse. You could start at the input side of the relay switch or the output side of the relay switch, or you could even start at the horn itself. The key is, if you were going to do this on the car, you would choose an area that's easy to get to. Most times, the fuse boxes are easy to get to, but sometimes the relay could be buried behind the dash, and the horn could be right out in the open under the hood. But other times the horn could be buried in the fender, and the relate could be right in the fuse box under the hood, where it's easy to get to. Since you don't know exactly where the problem is in that path, when you're first starting, it's usually best to pick the easiest to access point and then on Lee, go to the more difficult to access points if you need to. In this example, since the Horn is working, what it's doing is it's telling me that this relay switch had to close because if it didn't close, I wouldn't get any voltage up to the horn and I wouldn't hear any sound out of the war. So I know I don't need to check the fuse in this case, but we still need to make sure that the full power were full voltage is getting to the relay and is getting to the horn itself. So let's start at the horn and if I was to make a voltage measurement from here to ground a voltage at measurement. I would expect to measure 12 volts here when this relay switches closed. Since these two horns Aaron parallel, this circuit is allowing both horns to receive 12 volts and a good ground so that they both sound loud. But in this case, the horn sound a little bit sick. Maybe it's the fault of the horn, but maybe they're just not getting enough voltage. When I make the measurement here at Terminal A at the top side of the horn, what I find is that I get nine bolts and since I expected 12 and got nine, that's telling me to look back in the direction I came from, which would be back this way to try to find out where am I losing that three volts? So what I would do is I would now come up to this location and see if I have 12 ALS that I expect there or do I only have the same nine volts that I had at point A. And when I come back to this location, I find that I only do have nine volts. So what does that mean? It means that we need to go further up the line and see where I'm actually getting the full 12 volts. What part of the circuit does have the full 12 ALS? So if I come up here now and make my measurement, I'm finding that I do get 12 volts at this location. So what this is saying is that if there's a 12 volt measurement at this location and a nine volt measurement at this location, then between these two points is using up three of the volts. And if I don't provide the full 12 volts to the horns, they're not going to sound as powerful as they're supposed to. By losing the three volts across the relay switch, it's making the horn sounds sick. So if you bought a new horn assembly and spent the money on that and put that in, you would not have fixed this problem because you failed to check that the horn was actually receiving its full voltage and it had a good ground. So in this case, the actual fault is the relay switch contacts itself. Sometimes over time, these context get corroded or pitted and it winds up, causing a voltage drop in the circuit where inside the relay, it's using up a couple of the volts. And if the voltage lost inside there actually was substantial enough, it might make the horn not sound at all after a while. But in this case, it was only robbing three volts, and that was just enough to make it sound sick, but not enough to make it not work. What if we had the same condition where the horn didn't sound right? But we actually were getting 12 volts here at the horn itself. So that would mean that the relay in this second example is not bad. It's actually allowing the 12 holds to get to the horn, but the horn sounds sick. So does that automatically mean I should replace the horn? Or is there still more to check? And the answer is yes. There is more to check when I get the 12 volts here at the Warren while I'm operating it. It does mean that the fuse and the wiring and the relay switch and the wiring up to the horn is good. But since the horn sounds sick, we need to determine if it's the horn or if it's the ground. So on the other side of the corn on the ground side, I'm expecting to measure zero volts because if this circuit is working properly, the loads will use up all the voltage. If I were to measure zero volts here, that would mean that if there's 12 here and zero here and the horn still sounds sick than it's the horns fall. But if I was to measure two volts or three volts or four volts here and I measured 12 volts here, that would mean that the two or three or four bolts that are measuring here is being lost between this point and the ground. And then I would have to just keep moving down the circuit. Perhaps I measure down here. And if I got that same three volts down here, that would mean that the problem is between here and ground, Geo one. If when I got down here, I measured zero. But up here I measured three. That would tell me that the fault of the lost revolts was between the ground side of the horn and this junction point in the ground distribution splice pack. There's always a measurement that can be made that will help you get the answer of what the actual problem is. You don't have to guess and say it's the horn or it's the relay or replace the wiring on the car or whatever it is you're going to replace. There's a way to make a test to confirm it, and it's just not that heart. So in the two examples we used here with a high resistance problem was in the relay context . And then, in the second example where the same condition horn doesn't sound right could have been either the horn or a fault in the ground path. You can see that the amount of measuring needed on the car would have been minimal, perhaps one or two tests, and you would have had your answer for whichever one of the fault it would have been. So in the next video, we're going to stick with this same schematic, but we're going to diagnose a condition where the horn doesn't work at all. So we'll see that most of our diagnosis in many of these situations can be done right here on the schematic before we get to the car. 22. 22 Horn Schematic Horn Inoperative: in this example are Horn is not working at all. So the first thing that we need to do is go over to the car and verify the condition and see if we can detect any clues if I go over and hit the horn switch on the car on the steering wheel. So that would mean on pressing or closing this switch. I'm expecting that the horn should work, but there's something else that I need to listen for. I want to listen to hear if the relay is clicking and if the relay is clicking. If I can hear an audible click of the relay, but the horn still doesn't work, that would tell me that this control side of the circuit is working whenever you're trying to diagnose something that's a relay circuit. If you can hear the relay click, then that's giving you valuable information that you don't have to check the control side of the circuit. But in this case, when I go over a press, the warrants which I do not hear anything, so that means that my diagnosis needs to start on the control side of the circuit. I don't know how many times I've watched people diagnosis a Warren circuit or a relay circuit where there is no click of the relay and they still go over to the other side of the circuit. The fault is not gonna be on that side because the control side needs to operate in order for the switch side to function. So whenever you don't hear the click, that means find out what's going on on the control side. So that's what we're going to do. If I was testing this circuit, since the load is right here in the middle, the relay coil, I would expect to get 12 volts along this path up to the relay coil and then after the load . Since this is the only load I would expect to have zero volts all the way along the rest of this path. Now there is one other thing that we can do to save ourselves from testing on the car on this particular circuit because there's a body control module that also has Theobald city to turn the horn on. If you remember, when I explained how this circuit worked, we were talking about the description and operation and how that suggests that hitting the remote panic button will send a signal to the body control module from the theft deterrent module to turn the warren relay on. And the body control module would then pulse the horn circuit on and off to activate panic mood. Can I use that to my advantage here in my diagnosis? Since I'm trying to diagnose the control side and the possibility exists that it's just a bed horn switch, it could be something else. It could be the wiring along the path or the relay coil, or even the power side or the fuse. However, could I hit the panic button on the remote and see if I get the horn to sound? Because if I do, all I'm doing is using this switch to activate the warren instead of this switch. And in this case, when I hit the panic button, the horn actually does sound. So what does that tell me? It's telling me that this path from here all the way up to here and then making a turn down this way, all of that is good. And then it's also confirming that the whole switch side of the circuit is working in this particular situation before, I've even had to diagnose anything on the car other than just hitting the warrants, which or the panic button. I've eliminated all of this and all of this on the car. And my diagnosis on the car would be from this point to this point. If you did need to diagnose this on the car, you would need to get access to the horn. Switch itself. What kind of voltage reading do you expect to get on this wire before you hit the switch? And if you notice on this circuit, you measure 12 volts when the circuit is on or off, but on the ground side of the relay coil. Since the switch is in the ground path, you're gonna measure zero volts when that switches on and you're connected to ground. But if that's which is open, you would measure 12 volts over here. And while that switch is open, you would actually measure that same 12 volts all the way along the path up to this point of the switch. And then if you came over to this side and put your vote Peter from this point to ground making a voltage at measurement. You would expect to measure zero if I was diagnosing this and I put my volt meter lead on this wire that's going to the switch. If I saw 12 volts on that wire, that would tell me that from this point of the circuit, up to this point is good. And if I saw zero volts on that wire, that would tell me that the fault was on the way back towards that point. But remember, I know the circuit is good up to this point because it worked when I operated the BCN and the panic button. If I measured zero volts here, that would tell me that the fault is in this area. And if I measured 12 it would mean I now have to decide if it's the switch itself or if it's the ground and one of the easiest ways to test. If the switches working is use a jumper wire to bypass the switch, you would use the jumper wire as if it was the switch, and you're just connecting a wire that goes from one side of the switch to the other. And even though you're pressing the switch it's possible that the contact inside is either broken off or damaged, where it's not making contact from this side to that side. So if you use a jumper wire to bypass that same circuit and then it works, then you know that the horn switches bad. And in this case, when I use that jumper wire and went from one side of the horn, switch to the other. The horn sounds that's confirming that I need the horn switch, and this is something that you definitely want toe get an understanding of. Maybe you're doing the work yourself when you get down to these last steps and maybe you're not. But if you've diagnosed from the schematic on your own, and you know that just by hitting the panic button, the problem has to be between this point. At this point, if you were bringing your car to a repair shop because you didn't want to take your horn switch apart or the steering will pad because it's part of the air bag. If you were bringing it to a repair shop and they then told you you need a BCM or you need a horn assembly or a horn relay or whatever it is, you would know that they're not correct, and either they don't know what they're doing, or they're trying to cheat you in some way. So regardless of if you're going to do the work yourself for not having this knowledge of understanding, the schematic can narrow down so many of the possibilities that it puts you at an advantage for when you're going to be diagnosing or repairing yourself. Or even if you're going to bring it to a friend or a repair shop. Because now you know and understand what the possibilities are. And an educated consumer really saves money over time. In the next video, we're gonna look at a different situation where the horn is on all the time, and the way that you go about diagnosing that is going to be a little bit different than what we've been doing so far. So I'll see you in the next video 23. 23 Horn on all the Time: in this case, we have the horn on all the time Now. If the horn was left on all the time, eventually it would drain the battery. So more often than not, somebody removes a fuse or removes a relay to prevent the horn from sounding. Or they disconnect the wire, going to the horn to stop it from sounding. Now that doesn't mean that there is still not a fault somewhere in the circuit. It's just disabling it so it doesn't make a sound, and we still need to find out why the horn is on all the time. The best way to get started with that is to decide what are the possible ways based on the way the circuit is wired. What are the possible things that could cause the horn to be on all the time? And as I look at this picture, I can see five things right off the bat that could cause the horn to be on all the time. So let's identify them. First off, if this switch was stuck closed, the horn would be on all the time because this switch would provide a path for the relay coil, which would then pull this switch over and then the horns would be on all the time. And the same thing would happen if the switch inside the BCM was stuck closed. So if we had a stuck porn switch or a stuff BCM switch, both of those could cause the horn to be on all the time. What if we had a short to ground here in the ground path, since this side of the relay coil normally does not have a ground path until the switches air closed? What if this wire rubbed up against the metal on the car and created a path to ground there ? If there was a ground here on this wire all the time due to rubbing and touching metal, then this relay would activate. Pull the switch over and the horn would be on all the time. So that's the third possibility. There's also two possibilities that are on this side of the circuit that could cause it to be on all the time, and one of them is the relay switch itself that could be stuck where, even though this side of the circuit is no longer active, this switch arm here stays connected and doesn't release back to the off position. So if that was toe happen, regardless of if you were pressing the switch on this side or not, the horns would still stay sounding because this switch is then stuck in the closed position. So that's the fourth thing that could cause it. But there's one other thing that doesn't happen quite as often, but it is a possibility. What if there was another 12 volt circuit nearby in the same harness and the wire for another 12 old circuit? Let's say there was 12 volts here from another circuit, and the wire was rubbing up against this wire that goes to the warn. If that 12 volt wire rubbed through the insulation and then rubbed through the insulation on the horn wire, the copper of the conductor touched each other. Then the 12 volts from that other circuit would power up the horn, and if that was happening, the one would be on all the time. Now that we've identified those five possibilities, the way you find out which one is causing it is by eliminating some of them in some fashion . One of the ways you could eliminate some of them is by pulling the fuse here. If I was to pull this fused out, that would stop the horn from working unless it was being caused by 12 volts coming from a different circuit powering up the horn. So if I was to pull the fuse out and the horn stopped, then that would eliminate this 12 volts from an external circuit being the cause. If I pulled the fuse out and it stayed on, then that would mean that the fault is that other circuit powering up the horn. But pulling the fuse out and it going off, it doesn't mean that it has to be the switch, but it means that one of the other four possibilities air still the culprit. But I've eliminated possibility number five. Let's say that when I pulled the fuse out, the horn does go off. So now that I've eliminated possibility number five, we have to narrow down the other 40 and by the way, when you do start your diagnosis and while I shouldn't have to mention this, I've seen people do this. The car came in with the horn disconnected and people spend time trying to diagnose it and they never plugged. The warned back in, and then they're They're wondering why they're not getting the results that they were expecting. So if I wanted to decide if it was the switch side that had the fault meeting, there's a shorted switch here where it's remaining closed or if there was a fault on this side of the circuit, what I could do is I can take this views out and what could I listen for when I remove that fuse? What would be happening if this side of the circuit was on? Because there was either a short to ground here or this switch was stuck closed or this? Which would stuff closed when I remove this fuse? I would hear the relay release if I was to take that fuse and plug it in and take it out and plug it in and take it out. If the fall was one of these switches or a short to ground on this control side, I would have the relay clicking on and off as I did that, because normally if I was to take that fuse in and out as long as everything is in the off position, and there's no short to ground. Taking the fuse in and out would not make the relay turn on and off. So by removing that fuse, I can tell if the fault is in the control side or if it's in this switch side of the circuit. In this case, when I was taking the fuse out, the relay did not click off. By doing that, Lee eliminates the short to ground, possibly shorted BCM switch possibility and the shorted horn switch possibility. And since we've already eliminated the possibility of the 12 volts from an external circuit powering up the horn, that leaves the only culprit being the relay switch. So in this case, the relay coil and switch are all integral or part of the relay itself. So the fix for this would just be changing the relay. But notice how you're not doing that much. Diagnosing on the card, I removed a couple of fuses and I just listened and used my understanding of the circuit to narrow down where the fault has to be. The more you practice these types of diagnosis, even if you don't have something wrong with your car, you can still practice and decide well, what could cause this circuit to be on all the time or if I had the horn or the cooling fan or whatever schematic you're gonna pick up and look at. If I had this circuit not working, where would be the best place to check? Or how does this circuit operate? How many switches are in this circuit that could turn this circuit on? If you spend some time doing that type of diagnosis and spend some time getting an understanding of the different circuits that are on the car after a while, you'll pick up a schematic and you'll quickly identify what you need to check what you can eliminate quickly. And if you then take this training and take it to the next level, where you get some hands on experience, you're well on your way to understanding the electrical circuit on your own car. Or, if you're trying to do this for a living, you'll have an understanding that can get you started and get you in the door to a repair shop, where you can show them that you know what you're doing. 24. 24 Thank You: in this video. I wanted to take a minute just to say Thank you for purchasing this product, and I hope it's giving you the beginning steps of understanding how to read electrical schematics. And if you've practiced this and found some additional schematics on your car and looked at them and applied what I've taught you in this course to try to understand them, and especially if you found the description and operation for your particular manufacturer and if needed. If you found the few pages that they give you most of the time on what the symbols on their schematics means sometimes when you're starting out and you're not that familiar with that many of the symbols it's helpful toe have that information as well. While it does take a little more practice in the beginning to understand a new schematic when you pick it up for the first time, the more different schematics that you actually look at, the quicker and better you will become at identifying what you need to identify on that picture. So moving forward in this short course, I wanted to communicate to you the basics of what you need to get started since this is an introductory course in the future, if there's any other courses or circuits that you feel would be worth investigating, if it's something that I could make a course out of and there's enough demand for it, I would be happy to oblige and help out people as much as I can. And if you have any questions about anything that you've learned in this course or anything you'd like to see and you'd like to contact me, you can reach me at Auto Electrical e D. U at gmail dot com. So I look forward to hearing from you. Let me know what you thought of the course. Let me know of any other courses or more detail or more explicit information you'd like to see in another course that maybe specializes in one area of automotive electrical. And I'll be happy to investigate those possibilities and see if I can provide something that will be beneficial to you. Thanks again and have a great day