Problem: all lights behind the cab are dead.

Symptom: Dead brake/tail/turn, reverse, license plate, and side marker lights. Trailer wiring still lights up trailer lights. There is one slightly frayed ground running to the 9 pin connector for the slide in camper, trailer's 4 pin plug ties into the same ground.

Truck: 73 F-250 Camper Special Ranger XLT 2wd w/390 and C6

 

that's funny because I just came in from the garage having the same problem. Mine all work for about 2 seconds then the back end lights go out though. I push the light switch in and pull it out again. same thing. 2 seconds on then off until I work the switch again. Maybe someone has an answer that will solve both issues. I'm thinking a bad ground or something.

 

I think they randomly went out while driving or something.

 

Lighting has been fixed. Wiring was bad. However, I have a new problem:

When I turn off my headlights, the only way to get the running lights and dash lights to turn off is to disconnect the negative on the battery for a second and put it back on. I've been told of a possible relay sticking, any advice? I just replaced the headlight switch and nothing changed.

 

Seeing that you have a Camper Special, do you have three relays mounted on the drivers side splash pan? These feed auxilliary lighting that was included in the camper special package. Perhaps one of the three is sticking, allowing power to backfeed into the lighting circuit.
Click on the .pdf link to see the relay location.

 

Is the relay you're talking about? I unplugged it and the lights go on and off like they should.

 

No, that's just a plug. It's one of two plugs (the other one's red) that connects the frame wiring harness to the main harness. The relays I was talking about are the three in the lower right of the illustration with the basic P/N of 14677. Your truck may or may not have them.

 

Looking under the hood, I don't see a row of relays in that area. However, I had a thought: if the plug I pulled connects the frame harness to the main, does the trailer harness tie into the main? One of the trailer wires is hanging loose. If that were ground, would that cause the lights to stay on? Pulling the battery ground shuts em off. As it sits right now, that plug is undone so could it be taking the trailer wiring out of the loop, thereby allowing the lights to operate as they're supposed to?