I just bought a new cargo trailer and pull it with a 95 F250. The 12v overhead lights inside the trailer wont work even when the truck is running and the headlights are on. Seven "prong" plug being used and have tried every combination of off on with the light switches. I heard somewhere that the constant power wire at the rear of my Ford may not have a relay or fuse in it and is made that way for some reason. Any answers?

 

that 12V wire should have a 20,25 or 30 amp resetable breaker in line,unless it,s factory it will have a big fuse under the hood in a fuse box,I could be wrong, Gigger. PS what does your owner's manual say?