A couple of thoughts based on my Coachmen motorhome of a similar vintage:
1. In my unit, there are a number of lights that are controlled by both a switch on the wall and a switch on the light itself. If one or the other switch is off, the light does not turn on. My solution was to disable the switch on the light.
2. If the lights are plastic ones with a slide switch on the light itself like mine, the plastic switch connects to the actual electrical switch in the light with an internal plastic connector piece. I had one of these get mutilated to the point where it wouldn't engage the internal switch properly. They could also conceivably get out of position and not work. At any rate, the outer plastic switch piece is held in with a couple of springy tab things on its sides and can be rather easily removed to fiddle with the mechanism (or the whole light unit can be removed from the ceiling by unscrewing a couple of screws under the diffuser) and the switching gear inspected and adjusted as needed.
To solve both problems at the same time, I removed the inner intermediate plastic pieces for the lights that were switched by wall switches, disabling the switches on the fixture (making sure they were set to the "on" setting of course!) and used some of them to replace the mangled ones in one or two other fixtures.
