My older brother runs his own contracting company, and primarily uses his 05 F250 to pull his 25 foot enclosed trailer around along with skid loaders etc. The interior lighting for the trailer is run using the constant 12v power terminal of the 7 pin RV plug that his truck came with. This terminal has no power switched or constant. All the fuses are good, and the connector itself is in good shape, I also chased the wire back to the cab and it was fine. Looking over the wiring diagram in his chilton its 12v source is a trailer/tow relay, I am unable, however, to locate this relay in either fuse panel. Using the diagrams in the chilton and the owners manual proved useless, also switching the horn relay with all the others did not fix it or locate any bad relays. Anyone have any ideas what the heck is going on?
It probably is a fuse, actually I think there is a couple that go to it. I used a little light bulb tester back there are just started checking fuses under the dash and under the hood.........took about 20 minutes.
The wiring on the trailer is a possibility, but all the fuses were tested, I found one bad one and replaced it but still no powah. The relays were also tested by switching them all out with a known good one.