Bad Ground Stumper

MPD56 wrote:
Interesting problem, you’re so close. I went on a Jayco tour and saw a model like mine being built; I watched and asked a lot of questions.
My guess is?
The ground wire going up, goes to one upper light and is daisy chained from there. I can only assume that the wire isn’t broken and it is the first connection. On my Jayco it is accessible (I think yours might be too). I might suggest that you remove one of the upper lights so that you can get at the wire and hook up a temporary good ground, this could confirm that all the grounds to the upper light circuits are good. This might give you another choice to ground the lights from another light if the one in the back is not accessible?

Good Luck

Added: a wire tracer is great idea,

The upper marker lights that these wires feed are located on the front and rear end panels. I suspect the pair of wires (one green hot, one white ground) goes up to the ceiling in the fridge chimney, then splits off, one going forward, and one going rear. It seems like an insanely wire-intensive way of doing it, but appears to be the way they did.

I suspect that splice where it splits to go fore and aft is where the failure is. With power on the marker light circuit from the truck, there is power going to all the upper markers as measured with a long wire back to a good chassis ground point. There is no return path to ground, however, so I show 12v on both terminals of any given receptacle as the power tries to find a ground path. If I can come up with a way to provide one, I darn sure will!