My 94 pickup has a wierd electric problem, the brake lights are linked to the running lights. When I step on the brake, the front marker lights and the dash lights come on with the brake light. If I turn the headlight switch on the lights come on and so do the brake lights, and it wont let me set cruise control unless I turn the lights off. I know it has to be a short somewhere, has anyone had this problem before? Are there any logical places to look? I am not really wanting to tear the entire dash off, but looking like my only option.

 

Just a shot in the dark with my foggy memory.

There should be a dozen posts or so about the same issue. Check all your bulbs, the switch and relay. But i'm pretty sure it was bulb thing.

Also don't need the whole dash out just the steering shaft cover and lowers.

 

At least one set of your lights do not have a ground so the current goes through a different set of bulbs (which lights them up as well) in order to light up.
I'd check the bulbs in the taillights first. If they're in the socket incorrectly (180*) or if it's the wrong bulb it will cause that problem. Next I would check the tail light plug to see if it has a ground with both taillight housings disconnected, if it does plug the housings back in and check the ground on the actual bulb sockets. A trailer light converter is also a possible culprit.

 

After a little more research I am suspecting the trailer plug in, mine has been converted to a flat 4 plug with very sketchy looking wiring. Will go check on it tonight

 

If you can't find a wiring or relay issue, I had my fuse box short, so I know that's a possibility. I don't have cruise control though but my brake lights were all funny.

Silly question, but did you check your fuses? That could be a clue if there's a short.

 

Yes the fuses were good, but the PO had a 30 amp fuse in there, which is a little scary. I fixed the issue, I pulled the rear lights and spend some time with a volt meter. There are 3 wires on the back of the brake light bulb, and I cut the plain green one. for whatever reason it had power when I turn on the headlights. works on one filament now.