[will slow gto]

Hi Folks,
A couple days ago I was driving my 69 GTO and noticed whenever I pressed the brake pedal, the underdash courtesy lamp and dome lamp would come on. Checking the fuses, the 20 amp 'Stop' fuse was blown. Popped another fuse in and it blew again in short order. I noticed that when the dome lamp came on along with the courtesy lamp, the dome lamp bulb was very dim. Started searching for some threads on here and one or two indicated they may have had a short in the dome lamp harness. Other posts indicated some slight oxidation on the contacts in the fuse block could be increasing resistance. I disconnected the dome lamp harness from the tail lamp harness and took some 200 grit sand paper to the 'Stop' fuse and also the 'Dir Signal' fuse as that had blown too and I no longer had turn signals. This improved the situation slightly but both ended up blowing again after a few miles of driving. The car has 64K miles and the only wiring harnesses that have been replaced are the engine harness and the forward lamp harness, but those were replaced about 3K miles ago. Perhps it's just coincidence but a small chunk of black rubber fell from underneath the dash about the same time these problems arose. I've included a photo of the small piece of rubber (next to key in pic), maybe someone recognizes where it might come from, are they related(?), I'm out of clues for now. Thanks for your consideration.
Will

[johnta1]

I'd look at the brake switch at the pedal?
Brake has power full time. Sounds like a short somewhere in that circuit.
Does fuse blow when put back in or when brake pedal is pushed?
That piece may have come from the switch.

[Lemans64]

Do the tail lamps work or brake lamps work after replacing the fuse, is there any funny function in the lights on rear of car or front for that matter.
Bad ground would do weird things as it is looking to ground out thru other devices causing low voltage on other devices. But should not blow a fuse.
also Blowing both turn signal fuse and brake light fuse would lead me to thing your have an issue with rear brake light, turn signal wiring or Bulb.
Yes could be just a bad Bulb. Replace the turn signal fuse and check to see when the fuse blows, right or left turn? Or just driving and not using the signals.

[will slow gto]

Thank you for the responses. I installed a new 'Stop' fuse and a new 'Dir Signal' fuse before I left for work this morning and when I returned home, they were both still in tact. I swapped out the brake pedal switch and it blew the 'Stop' fuse after depressing the brake pedal for several seconds. I did not touch the turn signals... I had my wife check the brake lights while I was depressing the brake pedal (before the fuse blew) and she said only the driver side brake light was coming on. So my guess is probably some sort of short feeding the passenger side brake lamps. Also thinking that the turn signal fuse blew because I had the right hand turn signal on for an extended length of time and ultimately that fuse heated up enough to blow. Any additional suggestions would be appreciated. The car is in great shape and has not been messed with but it is 50 year old wiring in the trunk so there could be some deterioration in the insulation.

[johnta1]

Check the right rear bulbs and for anything looking strange?
Corrosion in the outlets, etc.
Follow the wiring to rear seat area for anything strange. Maybe mice problem?

["QUICK-SILVER"]

Don't know if the dome light glowing, with blown brake fuse, was done on purpose by GM or just worked out that way.

Courtesy lamps are on a seperate fuse than stop/dome.

With blown brake fuse.. Courtesy lamp power passes through it's bulbs on to the common ground it shares with dome light at headlight switch and door jamb switches. Then backwards through the dome light into the orange stop/dome power wire.. When you hit the bakes that power now has a ground path through the stop light switch and on out to the stop light bulbs. It's just enough ground to make the dome light glow.

When this is happening, turning the dome light on, at the headlight switch, will make the glowing dome light go off.

Got to keep all this in mind when looking for a short in stop light wiring. A multi meter will show things that you'ld think shouldn't be there.

Clay

[Lemans64]

Would be having a good look at wires going across the back of trunk, that go to right side lamp. Turn signal and brake lamp usually use the same wire
from the turn signal switch to the back of car, so would be looking at wiring coming out of turn signal switch for power with brake pedal pressed. Looks to be a dark green wire that feeds the right turn and brake lamps, it comes out at bottom of column.

[will slow gto]

Thanks for the ideas and suggestions. There appears to have been a fairly obvious short circuit in the brake lamp wiring in the trunk. For some reason a previous owner spliced a small length of red wire the the bgreen brake lamp wire. The soldered junction was wrapped in electrical tape but the uninsulated end of the red wire was making contact with the inside of the trunk and short circuiting.

[johnta1]

Cool!
Glad you found it.

[Lemans64]

Probably had some trailer wiring or something along that line. But ya that would do it. Just make sure all the lights work now before moving on.

[will slow gto]

That’s funny. My buddy Jeff (geeteeohguy) said the same thing about the trailer wire when I mentioned it to him. I’m not old enough to remember when these cars were new and being used the way we use SUVs these days. Why couldn’t a GTO tow a trailer or small boat?!?

[Lemans64]

It could be used for that, like most modern vehicles, they can be used for what ever turns your crank.
But wiring the car back then was up to customer and As you can see it may have been a butcher job or
not quite a plug and play type job.