WShould not be too hard to find. It has to be between the light switch, and the lights, so most lilkey it is hiding in plain sight behind the front cap.
Armed with a multimeter, and some time, you should be able to start at the light fixture, and follow the wire back to the problematic relay, or whatever device they used.
You might search out a Rexhall owners site, other owners may have had that problem, and be able to put you straight to the answer....
Back to a 5'er after 4 yrs fulltime.
Pulling with a '14 2500 ram, 6.4 Hemi.
Montana High Country 31RE