96 1500 dies when lights are on

[Bundy]

ok, truck ran fine. stopped at a friends for maybe an hour, came out, started fine. as soon as i hit the brake, it stalled. starts right up and runs fine until you hit the brake or turn the parking lights or headlights on, then dies instantly. also, when u hit the brake, the dash lights come on dimmly. anyone have any ideas? reading similar posts, maybe an ignition switch?? any input is appreciated.

Bundy

ps. its a 1996 c1500,4.3,auto

[bamadam]

Originally Posted by Bundy

ok, truck ran fine. stopped at a friends for maybe an hour, came out, started fine. as soon as i hit the brake, it stalled. starts right up and runs fine until you hit the brake or turn the parking lights or headlights on, then dies instantly. also, when u hit the brake, the dash lights come on dimmly. anyone have any ideas? reading similar posts, maybe an ignition switch?? any input is appreciated.

Bundy

ps. its a 1996 c1500,4.3,auto

That seems to be the smoking gun pointing at a short somewhere.

There are several ways to start tracking down the short. Isolating sections by pulling fuses and seeing if things improve, etc.

But brakes AND parking lights?? Do you have a trailer light harness (pigtail)?? You might want to start there.

Good luck.

[Bundy]

the trailer light harness was disconnected and i even disconnected the tail lites completely under the bed also and still same thing. weird huh?

[klinn]

I would check some ground wires. Have you had any mechanical repairs lately, that would have involved removing ground wiring? I had a camaro once that would die as soon as you turned on the fog lights, traced it to a poor ground at the headlights, come to find out the car had just come from a body shop after a front end collision. Tightened the ground, problem was solved.

[bamadam]

Originally Posted by klinn

I would check some ground wires. Have you had any mechanical repairs lately, that would have involved removing ground wiring? I had a camaro once that would die as soon as you turned on the fog lights, traced it to a poor ground at the headlights, come to find out the car had just come from a body shop after a front end collision. Tightened the ground, problem was solved.

Sounds like good advice. A poor ground would cause weird feed back into the system.

[RainRider]

Put a special tuned ECM in my 96 Tahoe. Some weeks later, started doing similar stuff to what you're experiencing, then sometimes no problems at all. Put original ecm back in - no more problems. (verified ecm by re-installing bad one, to have problems come back)
Rain
Edit: Turns out this was not my problem - read on.

[RainRider]

The positive battery post has two connections on it. One goes to the main fuse block (read, almost everything) and the other to the starter and probably the alternator. I'm tired of looking thru the book for now, so not really sure how much the one going to the starter takes care of.
BUT! Exact same symptoms you have, and you can see I already tried the ecm. The internal connection, though the post screw seemed tight, the crud between that internal connection at the battery post and the battery acted like a resistor, an intermittent resistor. So, sometimes everything is fine, other times, when it is acting like a resistor, the voltage is dropped when other loads are turned on (blower fan, wipers, brakes, etc.).
So, to save you some time (hopefully) check/clean those connections at the battery. I had to disassemble the connections and the internal metal spacer to get the crud out, then made sure I used a proper wrench to tighten the post. Before fixing the problem, I was able to cause the ignition to cut-out by wiggling that inside connector at the positive post (had to have the trans in drive/emerg brake on cause the momentary connection break while in neutral was too short to cause the motor to die, but it would with the transmission load on it)
Good luck with it.
Rain

[Bundy]

Originally Posted by RainRider

The positive battery post has two connections on it. One goes to the main fuse block (read, almost everything) and the other to the starter and probably the alternator. I'm tired of looking thru the book for now, so not really sure how much the one going to the starter takes care of.
BUT! Exact same symptoms you have, and you can see I already tried the ecm. The internal connection, though the post screw seemed tight, the crud between that internal connection at the battery post and the battery acted like a resistor, an intermittent resistor. So, sometimes everything is fine, other times, when it is acting like a resistor, the voltage is dropped when other loads are turned on (blower fan, wipers, brakes, etc.).
So, to save you some time (hopefully) check/clean those connections at the battery. I had to disassemble the connections and the internal metal spacer to get the crud out, then made sure I used a proper wrench to tighten the post. Before fixing the problem, I was able to cause the ignition to cut-out by wiggling that inside connector at the positive post (had to have the trans in drive/emerg brake on cause the momentary connection break while in neutral was too short to cause the motor to die, but it would with the transmission load on it)
Good luck with it.
Rain

Ok, hoping this was the issue, i completely cleaned the connections and made sure they are tight(both positive and negetive) and still, soon as you hit the brake or lites, instantly shuts off. i also tried starting it in neutral, but soon as i put it in gear,dies instantly. a small note i noticed, sometimes when you try to crank it over, you need to turn extra hard on the key for it to crank over. im aiming towards an ignition, but they are pricey. any more input on this one?? thanks for all the input so far,

bundy

[RainRider]

Bundy,
On my Tahoe, and I think it's the same on your truck, battery positive goes to a post (remote battery stud) under the main fuse panel cover (nearest driver's door under hood). If voltage is dropping there when you turn on lights, then the connection there, or possibly the lead at the battery post where the wire goes into the side-post connector, is loose. If voltage is good there, (now, I'm trying to remember the wiring diagram) if you go to the instrument panel fuse panel (left side of dash, visible with door open), you should be able to measure for voltage there. Again, the voltage should not drop (a small amount of drop may be normal) when you turn on loads. With the problem you're describing, I think the voltage drop will be very obvious.
I'm looking at my GM (Helm) manual now.
You said it cuts out when you turn on the lights, if I remember correctly.
That circuit does not go through the ignition switch, but if you have a loose connection at the battery post or the remote battery stud, it can cause a major voltage drop.
See what you find there.
You'll need a voltmeter, or at least a test light for these checks, but then, loose stuff can really be obvious some times, when it's finally found.
Rain

[777stickman]

The Ignition switch could be a problem, but as Rain said, the lights don't go thru it. For your problem I'm thinking batt cables. They can get corroded. They can get cleaned and tightend and look great. The thing is that the corrosion can get into the cable part you can't see and cause alot of grief.

Try this. Turn on the headlights. Does the motor crank and lights stay on? If it cranks and the lights stay on then I'd say the ground cable is good. Does the motor start? If it doesn't then I'd say there is a problem on the positive side. On my '98 there are 2 pos leads off the batt. One goes to the starter and one goes to the "mega fuse" (175a) located on the pass side of the fan shroud. Out of that are 2 cables. One going to the alt and the other going to the "remote batt stud" at the underhood fuse block. These cables and the connections are the ones you really need to look at. The cable to the "remote batt stud" is what powers almost everything on the vehicle, IGN, ECM, lights, etc.

A little long winded, but I hope it helps..........Steve

[Bundy]

thanks for the replies !!! I will try your suggestions and let you know the outcome. i really hope its something simple.

thanks again,

Bundy

[Bundy]

ok, finally was able to get some time to look at the truck with your suggestions. i have good voltage at both fuse box locations and now here is where things get weird(er). the truck had a in-line trailer plug adapter, which was disconnected all along, but today completely removed it and cleaned up a ground wire on the frame near the drivers side rear bumper.....truck starts and is running....as soon as i unplug the tail lite at the rear of the bed, the truck dies... its got me baffled !!!

[RainRider]

"as soon as i unplug the tail lite at the rear of the bed, the truck dies"

Yeah, I can see how that can be confusing. I have no ideas about this one.
Good luck with it.
Rain

[mr_mushroom]

at this point, i'd take it to an ASE electrician. they should be able to help.

[RainRider]

Bundy,
Got to thinking about the pulling the rear lite.
If the socket is somehow shorting (I'm having to assume the lite is on) when you pull it, it can be a different way of causing the same thing you're seeing earlier - now I know that don't make a lot of sense, so let me just ask.
When you measured voltage at the connections you said you had good voltage at, did you have lights on, and maybe your a/c blower up to at least medium? Not trying to insult your intelligence here, but some would not think of that. With no load, even a bad connection will read full voltage.
Rain