I have a 1994 Chevrolet Silverado, and the rear brake lights and turn signals do not light when the headlights are on. All other times they work fine, but as soon as the headlights are turned on, they go out. I recently had to have the bed removed to replace a brake wire, could they have not rewired it correctly? Or is it just a short somewhere, that only engages when the headlights come on?
It is possible wires were damaged when the box was replaced, (or they may have wired it incorrectly) causing a short.
You can use a jumper wire (from the front to rear) to test all the rear lights (brake and turn signal) or remove the box and do a thorough search for a broken/crushed wire.
After the jumper wire is in place, activate the headlights.
Make sure everything is grounded properly.
I don’t see how the headlights would have anything to do with the brake and turn signal lights. Except for the headlight dimmer switch (part of the multi=purpose switch; signal stalk) they’re on separate circuits.
All the fuses and relays are good?
Remember to ensure the top center brake light wire is connected/working and in the clear (if so equipped), IF the box is removed again.
Please post back here with the results of the final repair would you?
The only place I can think of that a failure should cause that would be the light switch. I don’t know how easy it may be to change out, but mine takes about 10 seconds. If you can access the wire connections and you can find out what wires control what, you should be able to test it.
Sometimes there is a ground wire that screwa directly to the pickup box right behind the light assembly that could be rusted or hanging. Try a jumper cable from the bed to the cab and check the sockets too.
After a careful search, I did find that one of the rear wires was not grounded, the wire had come unattached. However I was still noticing the drain on the battery, so I took it to the local mechanic and he said that the radio amplifier was bad. Apparently they do not make them any more for my age of truck, so I found one at the local junk yard. This seems to have solved the problem, glad I took it in because I would never have guessed something like that. Thank you everyone for your help!