1987 GMC electrical problems

[westcasey]

I've got an '87 GMC 1500. I am having some weird electrical problems with it. First. the radio doesnt hold memory; every time you turn off the ignition the clock and presets clear out. Next, when you open either door (when the domelight button is released) the radio goes off. And..... When you honk the horn I get no sound except for a buzzing when the ignition and the radio is on; the horn will also make the domelight come on. Anyone have any advice where to start looking??? Any input would be greatly appreciated!!!

[87 STEPPER]

If your truck has an aftermarket auto alarm installed then remove it or disconnect it from the main power supply.

My mother inlaw had an old delta 88 and it had an alarm like a viper or something like that and the computer processor it has went bad and the car was doing all sort's of crazy thing's like when you turn the radio on the wipers would come on but the radio didn't and when you turned on the blinker's all the lights would go nutty and then out of no where all the power locks would start to go up and down and not stop until the fuse was pulled.

I removed the entire alarm system and spliced all the wires back that had been broken into to supply power and ground's to the alarm sys. and then everything went back to normal.

If you don't have an alarm installed then i dont have a clue what could be wrong.

Let us know what you find

[383drvr]

Yeah, see if it has an alarm installed. I can throw some ideas out from experience with my truck:

- Radio: If its stock, I dont know whats wrong... Right now, trace the power wires and see where they go. The power is probably connected to the wrong side of the courtesy light system under the dash, causing it to turn off with the lights.... If its aftermarket, it has to be connected to a constant 12v source. There should be a hot terminal on the firewall. I connected a new 14g fused circuit to this terminal for my radio and works great now. Sounds like you need to do this regardless. (cheap @ $15 from Autozone)

- I dont know what to say about the horn/dome light situation... Is the buzz coming from inside the car or from the horns themselves? Do the horns ever work? I think you need to trace the lines and see if anything has been tampered with... The horn wire is green and has a relay near the fuse terminal with a brown and yellow wire. The relay may simply want to be replaced.

- Dome: These are pretty simple to diagnose. They are orange/white wires. Check your grounds in the doorjambs, and the light socket under the dash. They go to the fuse panel and thats it; Nothing should be able to interfere with them. See if any of the lines have been tapped for power... Thats probably your problem there, I suspect the radio has been tapped into one of the wires... (common practice in older radios).

Let us know how it goes!

[westcasey]

Thanks for the info. The truck doesn't have any kind of an alarm installed. These problems are all linked together. The radio goes off when the door is opened and the dome/courtesy lights come on . The buzzing comes through the radio when the horn is pressed and the horn never sounds at anytime. I bought the truck through a local Chevy dealership. I contacted the man who traded it in. He said there were no electrical problems whatsoever when he traded it. So....I wonder if the dealership could have knocked a ground or something else loose when they went through the vehicle? The man who owned before is reputable and I know he would tell me if there was a problem before. Thats what makes me think that the dealership screwed something up.

[roempty]

sounds like something is crossed .I would start eliminating in order starting with radio disconnect power than see if this helps than disco the doom light and so on.maybe a bad ground but ,sounds like something got pinched maybe when dealer cleaned the truck GOOD LUCK

[blink32]

Ok, you eliminated it having an alarm, but what about the radio its-self? Is it a stock radio or an aftermarket one? Is there any kind of auxillary equalizer or amplifier? Any one of these could have been wired in the system incorrectly and causing your problems but would be one of the easiest to eliminate.

And it might just be the reason why the guy who traded it in got rid of it. If i broke some stuff on a car and traded it in to a dealership I wouldn't own up to it either if the next owner asked. I'd just let it be the dealerships problem.

[74Pumpkin]

I'd try looking at the fuse block and the mass of wires around it. Seems to me they all run from there and something might have happened if someone was working around it. If a small short happenened in there it could cause all those things and possably many more.

[westcasey]

Well.... I got the radio fixed. Took the memory wire and cut it. Spliced in a new wire and hooked in to the cig. lighter port in the fuse box. But no the horn doesn't work at all. I'll keep on after it.

[Grim Reaper]

So who installed that aftermarket radio? They used the dash light as ground on your radio possibly.

Check fuses as well. the symptoms indicate some thing is not getting power or gound and it's pulling it backwards though the electrical system. I would bet on the fuse being blown. Also I would see if you got juise on the cig plug. When horn, mem, dome and cig are out they share a fuse.

You use the ashtray as a coin cup? Look down in the cig plug and see if any change amde it down there.

Also a bad gound would cause this but usually the gages bounce with the flasher as well. THe ground starp is not hooked up off the passengerside head is 99% the find with bouncing gages.

[westcasey]

Its actually the factory radio. My cig lighter and all works. All fuses are good. The gauges don't bounce or show any problem. Im not sure what to do now.

[westcasey]

I got it fixed!! The horn and the radio work correctly now! The only thing that doesn't work is the upper dome light which is no big deal. Thank you all for your help!!!

[Grim Reaper]

Originally posted by westcasey
I got it fixed!! The horn and the radio work correctly now! The only thing that doesn't work is the upper dome light which is no big deal. Thank you all for your help!!!

Well what was the problem!. Post up the repair so incase somebody else has the same symptoms they will know what you did o fix and have soemthing to try.

[westcasey]

The memory wire from the factory radio was crossed with a ground. That had blown the fuse for the horn. So after I got the memory wire fixed, it dawned on me that the fuse for the horn had probably blown.