Chevy truck stalling

[Ccolvin]

My son has a 1986 Chevy K-10 with a rebuilt 350, MSD distributor, Accell coil. This past July, he had the truck completely repainted, which meant taking off the bed. PROBLEM: Recently, he has had to push his brake pedal for the truck to start, if he wants it to remain running, he has to turn on the lights....specifically headlights. Even with headlights on, when he comes to a stop, it wants to die unless you rev the motor and push harder on the brakes. We have checked out everything on the distributor, (except the wires from the coil to the module-will do that tonight) it gets 12V to the Batt connection, but a timing light shows it is mis-firing when the lights are off. Just in the last day or two it has started running more roughly even with the lights on.
Two further issues, (a)sometimes when the key is in the on position, the coil sounds like it is buzzing. (b)Also, the yellow wire from the light switch (which is the one running to the tail lights) is very warm to the touch.
Have checked the main grounds and others as we find them. It is not fuel or vacuum related as we have gone through all of those systems.

ccolvin

[gmsmallblockguy]

You probably have a pinched wire under the bed.
It deffinately sounds like bad wiring somewhere. You mentioned the warm yellow wire. That's a good start I'd be looking for something pinched or laying on a hot exhaust pipe grounding or shorting out.

[911S_TARGA_RSR]

Yah! I would definatly check for a grounded wire.

[Ccolvin]

Thanks guys, we haven't had much time to look for it, but will follow up on your leads, will let you know.

[Ccolvin]

Checked everything from the truck cab to back lights-no problems. Checked throughout the dash.....disconnected switches, checked ground and continuity of everything we could lay our hands on....still nothing. Are working in the engine compartment now.....But still no answers to why the truck only runs with the lights on. Anything else? HOw do you check the ignition switch?

[a1supersport]

Maybe he should have it painted again, and it'll go back to normal...just kidding . There is a diagnostic plug-in under the radio area of the dash. If you know a repair shop or dealer in your area that has the right diagnostic set-up for that truck, it might be worth taking it in...even if it gets expensive. I had an 83 Silverado 4x4 and it was an electrical mess, but it worked decent enough, so I left it alone. These trucks have wires upon wires that seem unnecessary. I guess you could say the 80's were the "infant" years of the electronic/computer cars.

[a1supersport]

There is a quick way to by-pass this problem. Find a 12-volt "switched" lead at the fuse box...preferrably one that's not being used, like an "ACC" (accessory) lead, and run a wire straight to the positive terminal on the coil. That'll make your coil "independent" again, and take the load off your electrical system (the lights and the wiring for it). From there the truck should run ok with the lights off, and the yellow wire shouldn't be warm. Yeah I know, it's a band-aid solution, but it'll save a lot of grief.

[Ccolvin]

You know, I have looked everywhere for that diagnostic lead and its just not there. There is nothing that even resembles it. I haven't looked for wiring colors to trace it out, just the recepticle. Your second suggestion is a great idea to try, even as a further diagnostic tool. Thanks! Let you know what happens. Question, suppose it doesn't help, would they lend suspicion to the ignition switch?

[a1supersport]

I guess maybe that even though our trucks are only 3 years apart, they may be totally different from an electrical (diagnostic) standpoint. But the "ACC" solution is definitely worth a try. It'll definitely work, but if your "yellow" wire is still getting warm, something's either pinched or is grounding out. Replacing the ignition switch would definitely be worth a try. After 17 years, it may need to be replaced anyway. Hope to hear that you've found the problem, good luck .

[Ccolvin]

We did connect a wire directly from the battery to the distributor and the truck ran fine...without the lights on. Then I went downstream and attached the wire from the positive buss on the firewall over the driver's side heads...it did fine. We repeated this process at each major connection point until we got to the ignition switch. I disconnected the ignition switch and attached a jumper between the hotwire from the fuse panel to the pink wire back to the distributor (of course, re-connecting the pink wire at the distributor) and it ran fine. We ran out of time to connect the input wires to the ignition switch and jump from the output post (on which the pink wire normally connects) to the pink wire---thus disconnecting everything else from the ignition switch so as to determine if it is the switch or something attached to it (such as aux, lights, etc.). That is the next step. But a1supersport-you put us on a good heading and we are making progress. Now, for time to complete the job!

[corvair]

you may want to go and get yourself a new ignition switch and just plug it in without installing it. they are pretty inexpencive and make sure you tell them if it has tilt wheel bacause the work backwards from each other.

[a1supersport]

Glad to hear things are progressing well...glad I was able to help . Have you taken it out for a drive lately? I'm kind of wondering about the "truck running more roughly", which might be a totally different problem. And the switch replacement sounds like the way to go. It's cheap insurance. And even if yours is still ok, it'll eliminate one "possible" problem. Good Luck, hope to hear good news soon .

[Ccolvin]

Well, we replaced the ignition switch and thought we had it, but it started up its old tricks! After going through everything, we finally gave up and took it to an auto electical shop her in San Antonio. It took them a week, but they found a short in the wire block that fastens to the back of the fuse box through the firewall. I had suspected that area, but could figure it out, and didn't have a clue as to how to repair it if I found something. Anyway, he is re-timing and re-tuning the carburator and is running the truck. Wow, what a wild and frustrating journey...but it is behind us now! Thanks for the input and hope all of it helps someone!