Is this a trailer or a motorhome or a truck camper?
Regardless, you have a bad or broken connection somewhere, or a blown fuse that you haven't checked. It could be a ground connection or a power connection. If it's a trailer or truck camper, the obvious first place to start looking is at the connections between the truck and the RV. If it's a motorhome, there might be a good deal of hunting around to do to find the problem; if you can get a wiring diagram, especially one that shows the wire routing, that might be very handy.
For motorhomes, occasionally they do odd things like wire the running or other lights to the trailer light circuits of the chassis.
