Chevy Truck - No Start, Flickering Lights & Gauges - Voltage Drop Testing (2023)

Introduction

In this video we show a classic example of ground side voltage drop causing a no start on this 99 Chevy Tahoe. When you have more than one accessory that quits working all at the same time and a no start there is usually a common cause. A common power or a ground for example. Let's see what we find here. - Enjoy!

Follow up to this video, the repair: youtu.be/TAZOhZLEF0s

Mastering Voltage Drop Testing with Pete Meier and "G" Jerry Truglia: www.youtube.com/watch

The Trainer #47: What measuring voltage on the ground side means: www.youtube.com/watch

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Content

Their viewers and welcome back to the cell phone Auto Channel yeah this little Chevy Tahoe and it seems to be possessed, as you can see, with the flickering lights, so the headlights are flickering the 4-ways turn - so you can see our flickering along with the under hood light.

It's like a little bit of a disco, so currently, what's going on, is I had the four-way flashers on, and this is what you see now.

This is not the only problem.

The vehicle has reason it's here is because it came in on the hook, the guy started.

It made it about two miles from his house and car quit, but he did notice when he turned the 4-ways on the dash lights were flickering, things were buzzing sounded like the radio was on I'm gonna, show you what I found I'm gonna show you what the problem is or where I'm heading with it, because lo and behold the tow truck drops it off.

It runs perfect, which is always the case, or so it seems so, let's see if we can figure out.

What's up so, unfortunately, when you get cars like this that are seemingly possessed, they tend to fix themselves.

Sometimes you got act quick when they're acting up, but this is what it does with the 4-ways on now I'm going to take turn the headlights on.

That's what you get in here.

You know there you get nothing, you get no headlights just get some buzz and going on and then you've got this now.

I'll take a turn, the key on already with the keys.

Let me find them boys losing keys.

Oh you know where they are right here in my pocket.

So let's see stupid, chevy keys.

So that's what the key on turn on the blower motor and that's what you get I.

Also noticed you have no window opera, oh don't let it go to the window lots of buzzing going on here.

So we have lots of functions that don't work, including the car won't start it'll crank, but it will not start okay, so I'm gonna leave it broke.

Let's turn some loads on.

Let's turn our core weights back on I'll shut, the key off this thing's, don't explode! What do you think wild man? Ah, what do you think it is this? What do you think wait? We think smear with it.

It's a junk Chevy! That's my boy bringing them up right, all right! So all Chevy, jokes, aside and I know some guys get pretty sensitive about that I, really don't care personally, they're all junk.

In my mind, windows, blower motor headlights.

You know we have a lot of things that aren't working, so we could have a common power source.

You know battery, but the car does crank over goods.

Alright, you know I, don't suspect the batteries that or we can have you know a ground.

That's failing particularly a body ground is what I'm thinking, because most of those accessories on the inside are going to use your.

You know your G 200-300 grounds body grounds internally, so with a load on it, we can check for volts drop.

We can actually grab a meter or, if you're me, you're gonna grab the Handy scope on a rope.

I haven't hooked the battery positive.

Now we come over here to the engine and I'm, not seeing the flickering that you know we're seeing on the other like it may look like in the cameras that we are.

Let me try to isolate this, so this is only 780 milliamps, but that it's nice and bright now we'll go to the body which you know.

Of course support here should be connected to it and we can see the light intensity flickering.

The frequency of the flickering change, I'm, just gonna, add this light here body ground and we see we have the same problem.

We remove it quits flickering.

So what we can do the weight for this car tacked up so I'm kind of happy.

Let's take I'm gonna get a ground wire here.

I'm gonna go right off the battery post.

So now we have, you know but ground, look to our test light I'm, gonna, taking stuff that the core support and now everybody's happy.

So the four ways are flash normal.

We removed the ground and now we start getting our feedback.

So we could prove this with a meter which I can show you just for the sake of showing the way to do a proper voltage drop test fight.

It Leslie, we gonna, do it you just like proven stuff.

Stick it in the wall outlet at home, it'll education when I was a kid.

I did just that.

My dad.

Had you know you don't grab sunny? What did she do so? He would tow me in the junk cars.

Well, it's one car he towed in.

He had it had a strobe light on it, so under the yellow, flashy lights and I, wasn't really aware of the difference between DC and AC multicam time so I went down in the junk era.

I took that light off the truck and I was gonna hook it up in my room party, you know and I plugged it in I took him to strip the wires back, stuck him in the wall outlet.

It didn't work.

Needless to say, and I probably could have been electrocuted, but it was one of those stupid things.

I did as a child, unlike you who never does anything wrong right.

Right kind of car you're gonna get not that me for gonna, be it for a guy for tough, you like what its product.

That's what your dad drives.

We always like what our dad rides, except in my case cuz.

My dad drives a Dodge, so we're gonna print out the meter.

We're gonna put it on voltage.

I'm gonna use a plain old, plain old meter here, hopefully you guys can see it usually I use the snap-on, because it's easier to see for you guys it's the same.

Auto-Ranging I, don't know work a year since I've used it alright, so we'll stick it on a voltage scale and what we're going to do is measure the difference between the battery negative and the body ground, which is obviously our problem, and we should have little or no voltage drop if the system is good and functioning so the best place to do this is right off a negative battery.

Cable now I know for a fact on this vehicle, because this is a dual terminal battery that side post bolt.

It's a cable there is no voltage drop.

I know that.

But that is a potential for Bulls drop.

So if you're testing this, you know, let's say with a top post you're gonna have to go from the post to the terminal.

First before you can assume you can hook to the terminal, so assume I've already done that for know that I've already done that which I haven't but I just know it's good just because it's dual post it's easy to get to and then we're gonna go right to the terminal.

The bolt that sticks out there and we're gonna go to the cable, sir.

Well, the cable actually hooks to the truck.

So we can go.

You know from the upper post to the lower post, make sure that's good and then from the upper post to the engine.

Block and I'll show you our readings.

Alright.

So right now we're on the upper post on a dual post battery.

Technically, we should make sure that this cables good.

So we can just skip everything and go voltage.

Drop right to the engine.

I guess is what I should have said.

Sometimes, when I think I get confused and you can see, we have zero volts voltage drop, which is good, that's perfect, so now being that, we know that our connection here, the battery is good and the you know the studs good and the cable to the engine block is good and of course, there's no load on it.

I would actually have to have gap and get in there and crank it to be a hundred percent certain, but we do have the load of having the 4-ways on right now so I'm going to take and go right to the core support here, I'm going to scrape off a spot, let's see if we can get right on there.

Let me clean off a spot here that, where we can get good all right, so I've got a clean spot now, so we can see the volt meter.

It is on the voltage scale.

Let me just see so we can see that we have about well.

Of course that's gonna try to arrange on is here, but we got about four or five volts of voltage drop.

Let me flick on the headlights to add more of a load of a steady load.

Instead of this flasher lights are dim ones bright ones almost out.

We should have a pretty substantial amount of voltage drop and we do six point three volts is the difference between the negative battery terminal and the core support, which is hooked to the entire body.

So long story short, we just have a bad main battery body ground.

So there's a lot of videos out there on YouTube on voltage, drop I'll, see if I can find some post them in the link.

I think Peter Ritz motor age has actually done some and some of the other ones that I've seen it seems to be a kind of a topic.

That's always beat to death, but very rarely do they show application.

You know car comes in, you know now, if you guys do a voltage drop tester, that's your problem.

You know, so you know granted it's something.

That's always preached it's one thing, I think we've done some videos on ourselves.

I think we did one where we had some voltage drop on the positive side of charging system on all their so main things to know when you're doing voltage drop.

You is.

You have to have current flow, for example like when I Oh on the negative battery to the engine block.

You know really.

We should be cranking on it at that point, but in this case we're having problems with body accessories either the voltage drop.

You know to the body.

We obviously have a main ground.

That's gone plooey on us.

What I'm gonna do I had some heavier gauge jumper wires.

This is probably not a good idea, because I don't know how much current we're gonna flow through this, but we're gonna do it anyways here this is SMA.

This is what we do we'll find something shiny on the body.

We can go right from the engine blocks, I'm sure the ground goes to the block and then from the block to the body.

There we go we're good now, yeah just leave it there call it fixed ship it alright.

So, theoretically, this truck should start.

Hopefully it's not skates, but either that or I'm we're couldn't carry enough ground.

Not look like it's still.

You know, I turn on the four ways you know, I think we just you know, ended up with a cruddy connection.

Now that we have some load on it, we can redo our whole thing.

Strap and I.

Show you what it's all goods gonna look like.

So here we are with an engine running around installed.

We can see, we've got about 700, millivolts Oh point seven five holes how's, that for the headlights and everything on here I'd like to see that a little bit better end of the road baby, so we'll grab our wire back.

It's my extra long jumper, where you get that out of the way.

Oh, let's see, let me find the light where's, my flashlight, you see my flashlight Gavin huh, oh it's in the truck you saw so you guys unlock it.

This thing's got stupid aftermarket alarm on it.

Grab that pleasure yeah bring it over here son.

Let me see that whoa, it's quite the wild haircut.

Your mother gave you what do they call it? They call it the shave one side flick to the other side old guys do that when they're bald, you know it's called the comb-over.

It's on these cities.

We have the negative terminal that goes around town goes down, goes straight back and hooks to where the fuel pump used to be so.

It hooks right there where the old fuel pumps used to bolt to on the old carbureted days, so it bolts there.

Now that's our engine ground now I believe that little mess back there oops.

Hopefully you guys can see that so that braided cable goes back there to the frame from the frame up to the body that is our body ground or what used to be our body ground? Don't you give that the classic creature out here see if thinking you guys set up? So what were you thinking? Voltage drop was like when you crank it over.

That's that's actually a valid test, so that is one thing that we do when we're testing you know the battery and cranking it over to make sure it stays above that 10 volt margin.

So but ya know that's good thinking.

That's kind of like voltage drop right alright, so we have two potential problems here or what could be a problem where we could isolate where the voltage drop is you know, obviously it has to be or it could be from the engine block to the frame that that could actually be good or we could have voltage drop from the frame up to the body, so we can narrow that down and either way both those cables are looking pretty ratty in my opinion.

So if we want to further isolate this, I've got the scope on a rope hook to battery negative I.

Have the headlights turned on or a load put on the vehicle we go to the engine block? We have no voltage drop, otherwise we would have current flow through this light.

You know if we come to the body which plants I'm shiny, she should light up on us, even though we're going negative to negative, but there's enough potential difference there to flow some current.

Through that light.

Now we can isolate or further isolate.

Is it this wire coming from the black to the frame or from the frame to the body? Now, if we go right on the wire here to the engine block, we can see our test light lights up.

Let me turn off this light.

I'll go right to the so that is the wire coming from the engine block and then, if we go to the engine block itself, we see our test light does not light up.

So our bad connection is from the engine block to the frame which ultimately leaves you know this cable that voltage dropped.

This one has voltage drop engine block is good, so our crappy connection is not here.

The frame it's technically had the engine block where it goes from the block to the frame from the frame to the battery I'm, probably the worst person to explain this I hope.

I explained it somewhat to the point.

Someone can understand that your best bet is probably go.

Watch somebody.

It was a professional explain, voltage, drop potential differences from ground to ground, it's a relatively easy concept.

Of course, I'm not one with the words, but you can do a multi drop testing on power sights and ground sides.

There is a reasonable amount of voltage drop that should be in a system depending on you know the gauge of wire.

Is it going through a switch? Is it going through a relay I would say on average, less than a half of all? That's what you're gonna want to see more than likely stuff like this made your body ground.

So if you're gonna see it down, you know below 100, millivolts, typically, and you know current flow there's a lot of lot of variables, but certainly below the 5 or 6 volts that we were getting.

We can see the obvious problem.

Voltage drop is big enough to light a Tesla which is always handy.

You know where, for whatever reason, this problem was intermittent, like I said, if it drops off, you know, say it's tarin I drove the truck around and thankfully parked in front of my bay in case it didn't start which I went out to started when it was cold and it didn't so.

We pushed it in and then it started, yeah I guess, that's it.

There was a couple ways you can fix this.

You can either go down there and the original source of the wire, which is probably what I'll do replace it.

Probably here in a while I, probably I, will replace both of those.

So it doesn't come back and haunt me if you're, you know working at home and you didn't want to crawl under there just run a new wire from the you go anywheres off the engine block over to the body.

Technically it should go to the frame.

I should restate that from the engine block to the frame, because there's other grounds that actually bolt to the frame so I could affect that.

So you should go from the block to the frame, then from the frame to the body.

You can do that wherever you choose to do so, having a lift available I'm going to a lot to replace it, where it's at I'm going to get new cable or make one but likely because it's 5:30 I'm not going to order one today, but I'll get one tomorrow and get this thing fixed up, I'm just happy that it quit nothing like no problems files.

You don't want to do that guy, because you know darn well if it got towed in its gonna get towed back.

So you try to recreate the problem.

Bastion yeah, my attempt at that was to lease it all get cold which seemed to help.

So that's it hope it helped if it didn't be sure to thumbs down this video, if not give us a thumbs up.

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