OK an update, I identified the cable coming from the battery. Went out and bought 20 feet of No4 cable ran that outside the camper as a test from the 12V hot side at the batteries to the distribution block. Checked it against the bare ground wire at the dist. box end with 120V on, got 12V. Shut 120V off that same end now dead but it still has 12V at the battery end??!!
I'm beginning to think this may be a ground problem, what else could explain it?
Thinking about trying a No10 wire from the battery ground to the dist box, any thoughts on that?
There are NO fuses unless they are buried deep inside the camper belly.
BTW the original cable from the battery is distinctly smaller than the stuff I bought.