The Trainer #73: Automotive Electrical Fundamentals - Improve Your Electrical Troubleshooting Skills

do you get nervous when your boss hands you a ticket that's related to some kind of an electrical concern it may be 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 motor age 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 number one how to read a schematic wine diagram it's a lot more than just looking where why the wire goes say from point A to point B or identifying the components that are in that circuit that you're troubleshooting but you want to be comfortable understanding what kind of readings you should get in those wires what those components are doing what their role is in that circuit number two you want to be comfortable using electrical testing equipment for most of us that's starting off with the digital multimeter and number three certainly not the least important you must have a solid understanding of the fundamentals of electricity and electrical circuits so let's start by talking a little bit about what makes up a basic electrical circuit the very first thing that we have to have an electrical circuit is something that we want to do the work I mean that's what we're building the electrical circuit for isn't it in this case we're using a light bulb as the example but we refer to any component that does the work in a circuit as the load the second thing we need is some type of source for that electricity how do we get that well that's a little story in itself we're gonna cover a little bit deeper in a moment but let's just suffice to say for now we're gonna call that our source which is typically the battery some may argue that when the engine is running is the alternator 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 gonna 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 connect it on either end to the battery but that's not going to be very practical is it we also have to have a way as 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 things 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 this for the vehicle systems 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 meet to be more precise on the negative side or an accumulation of atoms that have an excess of electrons those that have an excess are trying to shed that excess and those were the shortage are trying to recreate that balance and game-1 back so what we have is the potential between those two posts an electro-motive potential and when you measure your put your meter leaves your voltmeter leads across the positive and negative posts that's exactly what you're measuring you're measuring that imbalance that electromotive potential if we 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 really quick so quick in fact that that wire you attach would probably melt down very 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 thing as putting the wire across the two terminals of the battery isn't it and just like we see in the cars when that kind of a condition occurs the short circuit we're going to blow a fuse or we're going to burn the wire so we have a circuit protection device in that case a fuse fusible link or a circuit breaker that will always be on the positive side of the circuit now this is going to make you think a little bit I hope here we got a picture of an electronic control unit or ECM like the 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 role can't it so when you're looking at that schematic like we were talking about earlier you want to consider when a component like that what is its role in that particular circuit that you're troubleshooting is it the load is it the 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 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 nother section of the circuit and as operating is that control device I want to share just a brief word on parallel circuits parallel circuits I don't worry a whole lot about yes there are parallel circuits on the car there are series parallel circuits on the car there are series circuits on the car but when it comes to troubleshooting I'm really not focused on what kind it is except for one raising and that's what is shared and what is unique among the loads that can trip the components that are doing the work on that circuit for example if I have a series of lights and they all turn on at the same time like the exterior lighting for example if none of them work then I know it has to be a fault that's common to all of the lights are you with me if none of these work there has to be something common to all of those lights and I can focus my troubleshooting steps right there if it's something that only one bulb is out if only one bulb has failed well then I can look at the parts that are unique to that load what parts of the circuit what wiring what connectors what what switches are unique to that load that's not working and that's the only reason I need to know whether it's parallel or not okay before you start writing your head and turning off the video another Ohm's law presentation bear with me okay I'm not gonna ask you to do any math but this there's no better way to understand the relationship between these elements than reviewing Ohm's law and understanding what it does and what it means let's start with e the e of course stands for volts and we've kind of covered that a little bit already what is voltage voltage is electro-motive potential it's the imbalance between into 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 something refer to it like water pipes and that kind of thing I'm not going to do all that because I think that just makes it more confusing it's electromotive potential it is the power if you will that we need to break away an electron on 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 its electro moto potential so I'm what you what I want you to do is keep in mind that when you're placing your meter leads anywhere in the circuit anywhere in the circuit that's what you're measuring you're you're measuring the electro-motive 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'm measuring the potential between those two leads and on a fully charged battery there should be roughly twelve point six volts if I measure it on one side of the ground at the load and I go to another point on the ground well there shouldn't be any potential error should there so I should get a reading very close to zero we're going to talk about that a little more a moment the main thing I want you to try to focus your head around is wherever I place my meter leads when the meter set in the voltage mode is I'm measuring the electro-motive potential between those two leads okay next we're going to move on to I I of course stands for current now current is the actual movement of electrons through the circuit and we measured in the turn we measure in terms of amperage I couldn't tell you what the exact number is it's like something million electrons past a point over a given amount of time I don't matter I don't care I just need to understand that 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 of the circuits your current flow is going to be the same no matter where you measure it in the circuit and that can be a good diagnostic tool alright let's move on to the next item our R Z Z stands for resistance and is defined as the resistance to current flow anything that causes an obstruction or hindrance to electrons moving through the circuit 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 everything in the circuit has resistance the load certainly has resistance that connectors have resistance switch contacts have resistance even the wiring offers resistance to current flow in the circuit most of these items should provide minimal resistance to the circuit the only real source of resistance should be the load and that's a very important concept to keep in mind the only real source of resistance in the circuit should be the load and because it is the resistance in the circuit that's what's primarily determined the current flow through the circuit if I'm looking at a circuit that has a problem if the loads not functioning it's like it should it's because something is affecting the current flow through that load that's important to understand because most of the problems that you're trying to hunt down in the shop are going to be caused by something that changed the resistance in the circuit now a very easy example of that is when we have a blown fuse that's created and open in the circuit hasn't it so what is the resistance now through that circuit if you measure with your own meter you're gonna 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 like a rock isn't it but there's some minor nuances in between those two they can cause you just as any headaches and those are the ones that you'd like to learn how to find but before you go on about how to find them let's talk a little bit about some rules related to changes in resistance the first one I want you to understand is that in the series circuit all the voltage all that pressure will be used to overcome the resistance in the circuit now let's explain that a little bit just for sake of simplicity 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 consumed by each will be in proportion to the amount of resistance each source contributes to the total that's a mouthful all I'm trying to tell you here is if there's more than one source of resistance they're each going to get their fair share of that push of that voltage of that potential and it's not going to be hey wait let me take mine first and then you can have yours next things have an electrical circuit at the speed of light so instantaneous for them for the most part let's take a look at example again the only real resistance is the load so if I start off with a fully charged battery of twelve point six volts I should get around twelve point four or very close to that to the load well Pete what happened to the other point two then we say before that everything in the circuit everything has some kind of a resistance the wire has resistance where it connects to the battery has resistance where it connects to the bulb has resistance 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 small but they're going to keep you from getting a perfect 12 point six or whatever you measure at the battery it's not gonna be quite the same when you go to measure it at the low 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 this case we're using as example as 0.3 don't hold to that number it's strictly an example okay 0.3 volts why is there something left over there instead of a perfect zero again because there are other sources of resistance between the backup load going back to the battery the wire the connection points anything else that might be in line there of course in the real world we have the switches where the control devices everything it makes up the circuit that's going to have some measure resistance very small should be negligible but it's going to take something to get through some voltage to get through that so you'll always have a little bit left over on the ground side all right now let's take a look at this example if I now put in a series of bulbs and I apply again we're going to keep even 12 volts so source 12 volts voltage potential electrode of potential applied to that circuit each one of these bulbs have equal resistance so based on that log in multiple sources of resistance they're all going to take their fair share they're going to split that twelve volts up equally each one should get approximately four volts now if we use our voltmeter to measure it's going to look something like this as we move along the circuit with our positive meter lead with our negative lead at the battery my first stop will be on the positive side of the first bulb and I should read very close to why measured at the battery again we're using this for simplicity sake but remember what I said earlier everything in the circuit has some resistance 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 ball 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 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's 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 them I did not get the full voltage drop against that against that load there has to be something more downstream sure enough we go to the next bulb well measure eight going in four volts consumed by that bulb that should leave us with four volts going out finally four bullets going to the third bulb now everything has been consumed by the circuit just like that law says and I should have nothing left over by the time I might get dull now I shared with you that everything in the circuit has resistance right some of it's designed to be there the wiring is certainly designed to be there the connectors are certainly designed to be there or the control devices safety devices certainly the load is designed to be there but what happens when something that isn't designed to be there shouts to show up well these are the unwanted sources of resistance and these are the things that are going to trip you up if you don't know how to find them this is your most common problem with electrical circuits today there's 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 gonna be dim wherever the case might be here are some common sources we've all seen this a lot of corrosion around the battery that certainly causes a extra source of resistance how about connectors that are bad they overheat and burn we don't have a good contact there that's an extra source of resistance certainly corrosion and that conversion can go way down into the wire can be at the connector pins or gonna be in the wire itself perhaps someone did an improper repair and allowed moisture again and over time that's certainly going to affect the resistance of that wire and that's going to be an unwanted source that's gonna slow current flow all the way through the system now how are you going find that unwanted source of resistance don't go run down to that car that's sitting in your bay with your ol meter in your hand because you're never gonna find it here's what I want you understand there's 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 currents actually flowing through the wire and here's how I want you to think about this if you're not quite understanding what I'm saying imagine for a moment the positive battery cable running from the battery to the starter we all know that's a pretty good sized 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 gonna pass a lot of current through it when I hit that starter that's going to draw 100 200 amps so I need a nice heavy cable to carry all that current and I'd agree with you you do but if you take your o meter and you measure one into the cable to the other what kind of reading are you gonna expect to get 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 gonna measure about the same thing that's because there's no current flowing through it 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 and we're looking for that thief no matter how big or small they might be we need to do it dynamically the first thing that you might want to do to get comfortable with this is to see what voltage drop looks like for yourself and if you're working in a shop that should be very easy for you to do just get a so get yourself a battery a couple pieces of wire and an old lightbulb and wire it all up do what we did here measure what's going in twelve point four volts and then move that same meter lead over and measure what's coming out you should get a very small amount now your numbers won't be exactly what you see here first I want you to measure the voltage of the battery so that you know you're what you're starting with then measure at the positive side of the load that's going to give you an idea of how much extra resistance is along the path going from the battery to the bulb but you should be very close to what you measured at the battery and then go to the ground side again you're not going to be a perfect zero because we don't live in a perfect world there are other sources of resistance still to come so you're going to measure something on the other side few tenths now some of you may have already kind of guessed what I'm working myself up to here some of you may be kind of scratching ahead and wondering what I'm talking about let's see which group you fall into I want you to take a close look at this picture notice the reading on the multimeter it's not a voltage scale of course and it's measuring eleven point five volts the meter leads are placed the positive meter Li is on the alternator case or ground and the negative meter lead is at the negative battery post if you know why this meter is reading eleven point five volts and what that's trying to tell you well then you don't need to watch the rest of this video if you are not sure you have to think about it stick around we're going to explain that it's something next voltage drop or learning that voltage drop testing method was a challenge for me and I spend a lot of time doing some of the things I'm sharing with you today until I got comfortable with it but I'm still not a hundred percent sometimes I still have to step back a moment and ask myself what exactly is that meter trying to tell me and I used that example I just showed you to get texts to actually think about just how comfortable they are with this testing method I get a lot of people shaking their heads so if you're sure 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's start off with the diagram than we started with earlier now the negative meter lead is where at the negative battery post and we're gonna 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 laid down and the meter gives me your reading do you remember what I said you're going to be reading you're gonna be reading the electro-motive potential between your two leads that's voltage electro-motive potential okay when I go and place it at the positive side of the ball before it's actually gone through the bulb then I should measure what do you remember what I said earlier it should measure right about the same as why I measure at the battery directly I'm gonna lose a little bit because there are sources of resistance between the battery and that bulb so I don't expect a perfect match within a few tenths though is what I should see and then I also told you that if I now take that meter lead and they move it over to the ground side well that bulb it should be nice and lit nice and bright that bulb should have used all that voltage to push the electrons through it so it's going to use it up there should be very little left on the other side again we had point three in our dot and our examples but it doesn't actually have to be that number but it's only going to be a few tenths there are still things a long way back to the battery that is still got to push through right so you with me if you want to test this for yourself remember that circuit I asked you to make earlier add another bulb to it we're gonna classify that second ball was our source of unwanted resistance so what do you think is going to happen if I measure the voltage coming in on the positive side of the first bulb 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 gonna read next to nothing like I would expect no I'm gonna read something aren't I because there is another source of resistance yet to come voltage is split proportionally among the resistances in the circuit I don't know what the number is yet I can figure it out using Ohm's law but I really don't care what I know is I should measure something here because there is a second bulb in the system to the example I don't have an Extra Bold wire it in but I'm measuring negative at the battery and the positive measured just on the other side of the load so somewhere between that and the battery is another source of resistance isn't there and that's why I'm reading that 11.50 volts there's something between the case ground and the battery negative terminal which means probably something in the harness the cabling that's having an extra high source of resistance that's preventing that that pure vol that voltage to drop just across the alternator right so very 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 like that because now you're leaving out a whole huge section of the path back to the battery aren't you you're assuming that that's okay when in fact that may be exactly where your problem lies so instead make yourself up a 20 foot test lead so that you can get from one under the car to the other number three use the positive lead on your meter to take your measurements number four be sure the circuit you're testing is on this is also vitally important there has to be current flowing through the system in order for you to take a dynamic measurement 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 were testing a brake light issue then somebody's got to step on the brake pedal and if it's something that a system is only functioning when the engines 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 gonna guarantee you that when you're done you're gonna know what side of the circuit has a problem number one measure the system voltage of the battery number two measure the voltage at the positive side of the load as close to the load as you can get and then number three measure the voltage present on the ground side of the load that's close to the load as you can get now again I want you to remember this you want to get as close to the load as you can to take your measurements this is not always practical but keep in mind that if you spot a difference you have to account for the part of the path that you did not test all right so just keep that in mind remember your meter leads are only measuring the potential between the two leads so if you leave a section where you didn't place those leads well again that could be where your problem lies you must test the entire path okay now let me share with you some examples of the meter readings you'll see and what they mean first when you take your first test and you're measuring the voltage at the positive side of the load and you read zero point zero 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's say that you're trying to test in a lot of the fuel pump and you set up your leads in the connector is close to that tank as you can of course you've got the leads running from that connector through the tank and then into the tank to the pump so this way I want you understand in between the test leads if I go to the if I had 12.4 going in as far as I can go but then I go to the other side and reading a perfect zero well somewhere between that last test point through that wiring into the tank to the pump and then back out to the connector where I'm testing that's where the problem lies and that's where at the next that's right to go next the isolate where the fault is occurring if your readings on both the positive and the grounds normal then odds are there's a mechanical fault in the loge okay that's not the quite the same thing as having a blown bulb what I'm referring to here is if you're testing say a fuel injector and you're looking at the electrical integrity of the fuel injector it tests good but the injector is not working well it's not an electrical problem then is it it's a 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 haven't opened 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 tenths of a volt then you have a source of high resistance on the positive side you know I've been to a lot of classes and I've taught a lot of people over the years and the question always comes up 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 this myself I tend to go by current flow the more current circuits allowed to carry the more drop you're gonna be able to get away with okay but with that said I want to share this with you in my own personal experience I have never had a source of unwanted resistance caused a change of only a few tenths typically it's a marked change it's a couple of bolts and you're going to see that on your meter so don't don't hang up yourself over just a few tenths if you see something like this six point one volts instead of that twelve point four you were 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 in fact this is the more common of the two most problems occur on the ground side of the circuit anything that you get over that few tents it's gonna show up believe me if there's a problem there it's gonna show up so don't get yourself hung up on just a few tents one way or the other okay so how do you find the problem once you determine which side of the circuits it's on it's on that's very simple just like these guys are doing between their points in the circuit they're shortening the path you know your problem is between the two meter leads let's just say with the ground side example I know it's between the ground side of the load and the ground side of the battery we're using the schematic I'm going to look for in the next easiest place to try trace or test somewhere in between the two a connector if you will I'm gonna take another reading there on the ground side path if my meter returns to normal then I know I've passed the problem and now I go back the other way until I narrow it down to where that point is finally located so let me say that again if I have a problem in the circuit between these two points my first step is to find a point somewhere in the middle and move my meter Li closer to that point and measure again if I'm getting the same reading the same abnormal reading then I know my problem is still between the two test points right but if my meter reading returns to normal I know I went past it so now I'm gonna have to back up a little bit until it goes bad again and I'm just gonna go back and forth until I narrow down exactly where the source the problem is again use points that are easy to get to it'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 eyelet in your connector something along those lines or where somebody has made a mistake you know they pinch the harness between a component whether it's a seat rail or they put the engine back in and pinch the harness between the transmission case in the end a lot of things like that can happen you know and you'll get to that but in the beginning look for common points easy points to get to as long as it's between there your to original test points you're just breaking that down into smaller and smaller chunks let's take a look at a fairly easy example BMW backup lamps one is operational one is not okay what does that tell me as a technician normally they're both on and they would be wired in parallel wouldn't they so if that's the case I'm gonna 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 like we just described I measured the source voltage at the battery first and then I'm gonna measure directly at the load on the positive side of that left rear backup bulb I measured a perfect zero volts ground side I also measured a perfect zero volts where is the problem and what kind of problem is it well obviously I have an open circuit don't I I should be reading at least 12 something here at the bulb going into the bulb on the pods inside the circuit so I know I have an open circuit on the positive side of the circuit for the rear left rear backup ball now I can go back to my schematic again look at the unique portion of that to go further with my tests so between what I learn on the schematic and what I know about the car I can easily come up with the next place to test this harness is passing through the trunk lid and back into the body of the car that's a high wear area isn't it so let's start there I'm gonna look at the hinge side the trunk lid side of the harness first taking another measurement I get the same reading have I passed the source of the problem yet 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'm measuring eleven point eight seven it's not perfect but it's certainly not point zero one is it I pass the problem so we're 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 you set up that 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 like you might incur while you're actually working on a running vehicle that too can kind of mess you up a little bit so I'm gonna show you a way now that you can get rid of all that we're gonna start off with the method that I showed you for testing the positive side of the circuit again I told you put the negative meter lead on the negative side of the battery use the positive meter lead to check the positive side of the load first right so here's only one change I want you to make to make it even easier for you to use voltage drop as testing method I want you to make one small change to the method that I just showed you when you're testing the positive side of the circuit just move your negative meter lead over to the positive side of the battery remember testing the positive side of the circuit both my multimeter leads need to be on the positive side of the circuit testing the negative side of the circuit both my meter leaves and it mean to be on the negative side of the circuit I'm still measuring the voltage potential between the two points but now since they're both on the same side of the circuit there should be none or there should be very very little in fact you can even set your multimeter on the voltmeter scale said 2 millivolts why because generally I like to use about a half a volt as my go no-go for voltage drop most meters have a limit of what they'll read on their scale that's usually 300 to 500 millivolts so if I set it to milli about and I give it an L or a blank screen or the little dashes that's telling me I can't measure that much there's a problem and you can use that on either side of the circuit so let me say again if you really want to know if you have a problem or not you're using voltage drop it's a testing method all you've got to do is remember on the positive side of the circuit the meter lead should be on the positive side of the circuit if I'm testing the negative R the ground side of the circuit then my meter leads need to be on the negative side of the circuit I think we've covered quite a bit today and on Trainor that's all the time I got but I'll look forward to seeing you again next month [Music] you

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Keywords: #automechanika, chicago, motor age, the trainer, automotive repair video, car repair, auto how to, how to fix my car, auto tech, auto technician, auto service professional, engine performance, auto electrical how to, automotive drivability, obd 2, obd II, onboard diagnostics, auto computer, voltage drop, ohm testing, voltage testing

Id: 9oM8_U0rB9A

Length: 41min 29sec (2489 seconds)

Published: Wed Jan 03 2018