CGW3,
I did a lot of boat work before the depression and ran into situations like this a lot. Boats are worse than RVs for this.
The thing that was most helpful was a circuit tracker. I now have two. One is from a big name company and was expensive and the other is a CCV (Cheap Chinese Version) from Hazard Fright. Both work and I can hook on and pretty well follow a wire to where it might go. When I loose a signal, I start looking for what happened there and most often find it. This is not simple or easy to do, but it can be done.
For lights, you need to hook onto the hot lead with the light off and try to pick up the signal. The aluminum skin is a pretty good shield so you will probably have to work from the inside.
Matt
