Automotive Electrical

Do you get nervous when your boss hands you a ticket that's related to some kind of an electrical concern? It may because your electrical foundation is not as solid as it needs to be That's okay. We're gonna shore up that foundation in this edition of the trainer coming up next Today's edition of the trainer is sponsored by MotorAge Training Connect an online video training platform for the automotive professional If you want to become more comfortable at electrical troubleshooting There are three key areas that you need to focus on N Well, that's a little story in itself. We're going to cover a little bit deeper in a moment But let's just suffice to say for now. We're going to call that our source, w That's the source of the electricity for the circuits in the system I've always used the battery as my testing point. So that's why we're going to stick with that today Now we need to connect the source to the load and we do that by providing a path from the source to the load And then from the load back to the source We refer to the side going from the source to the load as the positive side of the circuit And the path returning back to the source as the ground side Once we've made that connection, we essentially have a working circuit. Don't we? The light bulb will certainly light up if I connected on either end to the battery But that's not going to be very practical, is it? We also have to have a way of controlling When that light bulb is going to turn on or when that load is going to function We do that with what we call a control device Now the control device can be a variety of t It can be a switch It can be a relay. It can even be the driver in an electronic control unit And it can be located on either side of the circuit. Can't it? Now last we have to have some kind of way of protecting the circuit against an accidental overload Now how is that going to happen? We'll just kind of stick in a little tidbit here How does the battery provide the electricity for the ve Well, it's a chemical reaction inside the battery that creates an imbalance So at the positive side of the battery There are atoms with very few electrons Or missing electrons to be more precise On the negative side are an acc You're measuring that imbalance that electromotive potential If were to connect those two posts say with a piece of wire We will provide a path for those excess atoms to get back to the atoms or those excess electrons to get to the side with a shortage wouldn't we? And they would do so Really quick so quick in fact that wire you attach would probably melt down very quickly That's caused by the current flow through the wire and we'll talk about that again a little more later on But now that I have a path connected. I'm restricting that movement through that load Okay If I don't if I have a section of the path on the positive side anywhere before the load That's going to bridge that gap to ground or make that path back to the battery Well, that's the same t And just I hope Here we've got a picture of an electronic control unit or ECM Engine control module and we also have a picture of a relay Here's the point I want to make remember we said the basic elements of the circuit are We have to have a load. We have to have a source We have to have a path connecting the two Then we're going to add some type of control device so that we can operate the circuit when we want it to operate And some type of protection device just in case the positive side of the circuit gets to ground when it's not supposed to What would you consider the engine control module? Is that a load? Is that a control device? Is that a circuit protection device? It can serve more than one roll can't it? So when you're looking at that schematic What is its role in that particular circuit that you're troubleshooting? Is it the load? Is it a control device? It's the same with the relay, isn't it? The relay has to be energized in order for those switch contacts to close Well, the part that is energized that coil That functions in a circuit all of its own and it's a load The part that closes and makes the contact is operating as a switch And that's included in a whole another section of the circuit and it's operating as that control device I want to share just a brief word on parallel circuits. I don't worry a whole lot about Yes, there are parallel circuits on the car. There are serious parallel circuits on the car. There'series circuits on the car But when it comes to troubleshooting, I'm really not focused on what kind it is except for one reason And that's what is shared and what is unique among the loads the Components that are doing the work If none of these work then has to be somet Okay I'm not going to ask you to do any math But t Voltage is electromotive potential. It's the imbalance between one end of the circuit and the other That's what's got to happen in order to get electrons moving to create Electricity to get that electron flow This is the force that does that And there's a lot of examples some refer to it is the Power if you will that we need to break away an electron one atom and force it to Grab another one from a neighboring electron. That's essentially electricity. Okay We measure that in terms of voltage We call it's electromotive potential So I'm what you want what I want you to do is keep in mind That when you're placing your meter leads anywhere in the circuit That's what you're measuring. You're measuring the electromotive potential between those two points Of your meter. So if I put it on top of the battery Positive to positive negative to negative Then I'measuring the potential between those two leads and on a fully charged battery. That should be roughly 12. 6 volts If I measure it one side of the ground at the load And I go to another point on the ground Well, there shouldn't be any potential there should there so I should get a reading very close to zero We're going to talk about that a little more in a moment The main t We measure in terms of amperage I couldn'tell you what the exact n It's I don't it doesn't matter. I don't care I just need to understand that's what that term is referring to if I talk about current I'm talking about the flow of electrons through the circuit past any particular given point Now for most All right Let's move on to the next item R is easy stands for resistance And is defined as the resistance to current flow anyt Okay That's the load for one But that's not the only source of resistance in the circuit. Is it? Now when we look at resistance, it's important to understand that everything in the circuit has resistance The load certainly has resistance So what is the resistance now through that circuit? If you measure it with your own meter, you're going to get an infinity reading, aren't you? And what happens if we take and Short that wire to ground before it goes through the load what's going to happen to resistance in the circuit then? It's going to drop But there'some minor nuances in between those two that can cause you just as many headaches and those are the ones That you'd We have a 12 volt battery And we have one bulb in the circuit the diagram I've been showing here so far That 12 volts is needed to push through The resistance of that bulb to push the electrons through that bulb Once it's done that once it's done its job of overcoming that resistance There should be nothing left on the other side of that bulb second rule In the cases of multiple sources of resistance The amount of voltage cons So instantaneous for them for the most part Let's take a look at an example Again, the only real resistance is the load So if I start off with a fully charged battery of 12. 6 volts I should get around 12. 4 or very close to that to the load Well, Pete what happened to the other point too? Didn't we say before that everyt The wire has resistance where it connects to the battery has resistance Where it connects to the bulb has resistance And what do we say if there's multiple sources of resistance? They're each going to take their fair share So those sources of resistance are minimal very small But they're going to keep you from getting a perfect 12. 6 or whatever you measure at the battery It's not going to be quite the same when you go to measure at the load. All right Now once that voltage that's been provided to the load Once that's overcome that resistance and it's pushed the electrons through and lights the bulb up There should be very little left on the other side in t We're using as example as 0. 3. Don't hold to that n Okay 0. 3 volts Why is there somet Again Because there are other sources of resistance between the Load going back to the battery the wire the connection points anyt It makes up the circuit It's going to have some measure resistance very small should be negligible, but it's going to take somet All right Now let's take a look at t So based on that law again Multiple sources of resistance are all going to take their fair share They're going to split that 12 volts up equally each one should get approximately four volts Now if we use our voltmeter to measure it's going to look something It's not going to be dead on the money all the way through the circuit Now I'm going to get that four volts is going to be used by the first bulb because it's taking its fair share, right? So if I move my meter lead now to the other side of that load that first bulb, I'm going to measure what's left eight volts Now as a technician that should tell you right away If you didn't know about these other two bulbs That eight volts is telling you that there'somebody downstream That wants its fair share It could be one bulb two bulbs three bulbs. I don't know But that's just telling me that my did not get the full voltage drop against that load There has to be somet We go to the next bulb. We'll measure eight going in four volts Cons Some of it's designed to be there The wiring is certainly designed to be there. The connectors are certainly designed to be there the control devices Safety devices certainly the load is designed to be there But what happens when somet There'some type of unwanted resistance somewhere in the circuit That's taking its share of that voltage applied and because it's taking a share that it wasn't intended to take or be taken The load ultimately pays the price by not having enough To push all the current it needs to function properly And it's either not going to work at all or it's going to work sluggishly or it's going to be dim whatever the case might be Here'some common sources We've all seen t We don't have a good contact there. That's an extra source of resistance certainly corrosion And that corrosion can go way down into the wire. It can be at the connector pins or can be in the wire itself Perhaps someone did an improper repair and allowed moisture to get in over time That's certainly going to affect the resistance of that wire and that's going to be an unwanted source That's going to slow current flow all the way through the system Now, how are you going to find that unwanted source of resistance? Don't go run it out to that car that'sitting in your bay With your own meter in your hand because you're never going to find it Here's what I want you to understand is a difference between static resistance and dynamic resistance There's a difference between what a circuit can do when it's not working And what you're going to see in the circuit when it is working When current's actually flowing through the wire and here's how I want you to t We all know that's a pretty good size cable, don't we? Why is it so big? You might want to ask yourself Well, we know intuitively that it's big because it's going to pass a lot of current through it When I a few tenths of an ohm That's about right Now I'll challenge you take that brand new starter cable and extract just one single strand of wire out of it And measure it again with your own meter You're going to measure about the same t It's a static measurement Would you take that one strand of wire and connect it between the battery and the starter and expect it to hold up? Once you hit the key Of course you wouldn't So if we want to test for that extra source of resistance if we're looking for that thief no matter how big or small he might be We need to do it dynamically The first thing that you might want to do to get comfortable with this It's to see what voltage drop looks 4 volts And then move that same meter lead over and measure what's coming out. You should get a very small amount Now your n It's on the voltage scale of course and it's measuring 11. 5 volts The meter leads are placed the positive meter lead is on the alternator case or ground And the negative meter lead is at the negative battery post If 5 volts And what that's trying to tell you Well, then you don't need to watch the rest of t And I use that example I just showed you to get text to actually t So if you're shaking we're shaking yours just now Don't worry. You're not alone. So let me see if I can clarify it for you and make it come to life Let'start off with the diagram that we started with earlier Now the negative meter lead Is where at the negative battery post and we're going to leave it there I'm just going to use the positive meter lead to test along the circuit And when I put that positive meter lead down and the meter gives me a reading Do you remember what I said you're going to be reading? You're going to be reading the electromotive potential Between your two leads that's voltage electromotive potential Okay When If I go and place it at the positive side of the bulb before it's actually gone through the bulb Then I should measure what do you remember what I said earlier? It shouldn't measure right about the same as what I measure at the battery directly I'm going to lose a little bit because there are sources of resistance Between the battery and that bulb So I don't expect a perfect match wit There should be very little left on the other side Again, we had point three in our and our examples But it doesn't actually have to be that n We're going to classify that second bulb as our source of unwanted resistance So what do you t It's not lit I should still measure what I showed you in the block diagram earlier Pretty close to what I have at the battery When I go past it though Am I going to read Next to nothing I don't know what the n I could figure it out using Ohm's law But I really don't care What I know is I should measure somet And that's why I'm reading that 11. 50 volts There'somet So very important to understand that this reading here is telling me there's a big problem And it's located where between my two meter leads Now let's talk about the steps to performing a voltage drop test First thing I want you to do is set your meter to read dc volts And then place your negative meter lead on the negative battery post as close to the battery as you can get and keep it there This is vitally important You have to check the entire circuit And if you're going to try to make a voltage drop test and you're working at the back end of the car Don't use a frame ground or clip it to the trunk or anything You're ass Otherwise, you're just taking a static measurement This means that if you're testing the horn circuit, somebody's got to push the horn button now You're testing a brake light issue Then somebody's got to step on the brake pedal And if it'something that a system is only functioning when the engine's running, well, then the engine needs to be running Okay, now let you understand the steps here the three tests I want you to take and i'm going to guarantee you that when you're done You're going to know what side of the circuit has a problem n 0 perfect zero Then you're looking at an open on the positive side of the circuit If the positive side tests normally and you move your meter lead now to the ground side and read a perfect zero Well, now you have an open between the test leads or in the load itself Now again, let me give you an example. Let'say that you're trying to test in a lot of the fuel p 4 going in as far as I can go But then I go to the other side and I'm reading a perfect zero Between that last test point through that wiring into the tank to the p Well, it's not an electrical problem. Then is it? It's a mechanical one Next If you're measuring the same thing at the positive side of the load as you did at the battery And you move your lead over to the ground side of the load and again measure the same thing that you got at the battery Two possibilities either the circuit is not on there's no current flow Or you have an open on the ground side somewhere between the load and the negative side of the battery If you get a reading anything other than Battery voltage at the positive side of the load lesser that few tens of a volt Then you have a source of high resistance on the positive side Pete. What's the spec for voltage drop? How much is okay and how much is not okay? And I've heard different versions of t It's a couple of volts And you're going to see that on your meter So don't hang up yourself over just a few tents If you see something 1 volts Instead of the 12. 4 you're expecting to see That's a problem You definitely have a problem between your two test leads Same situation here The reading I get at the positive side is normal But on the ground side it's reading other than just a few tents Same as I said before and in fact, that's very simple Just like these guys are doing between their points of the circuit They're shortening the path But if my meter reading returns to normal, I know I went past it So now I'm going to have to back up a little bit Until it goes bad again And then I'm just going to go back and forth until I narrow down exactly where the source of the problem is Again, use points that are easy to get to There's no need for you to start pulling seats out of the car and unwrapping harnesses Not at this point in the game Usually the problem is going to be located near an islet, near a connector Something along those lines or where somebody has made a mistake Normally they're both on and they would be wired in parallel, wouldn'they? So if that's the case, I'm going to focus on the parts of the circuit that are unique To the one on the right rear That's where meeting a schematic comes in And then I'm going to start my tests Just Well, obviously I have an open circuit, don't I? I should be reading at least 12 somet So let'start there I'm going to look at the No, I'm still measuring an open circuit So let's move on a little closer to the battery from there Now I'm going to the trunk side of that connector And now I'measuring 11. 87 It's not perfect, but it's certainly not . 01, is it? I've passed the problem Somewhere between where I am now and where I was last Is the source of that open circuit There you go Broken wire, easy fix Now I realize that this is a very simplistic example But if you're new or you're not comfortable with voltage drop These are exactly the kind of tests that you want to take Using this method so that you do become comfortable with it The first thing I want to stress is that you go ahead and you set up that makeshift circuit of your own Using a battery and a couple of bulbs and do the measuring among them So that you can see the difference readings that you get And get comfortable with what the meter is trying to tell you Then you can start applying it to simple diagnostic problems And then from there you can move on to the more complex Now that you've had a chance to experiment with that for a little bit I want you to consider this I've shown you a very fundamental way of doing voltage drop and it works very well There's only one problem with that test method Sometimes it can confuse people by the meter readings that they're getting And sometimes if there's a changing voltage Because generally I