Chinook RV

Rear passenger tail light has a ground issue. Does anyone know the routing and location of ground points for the white wires?
The previous owner ran a temporary ground fix to the grounding plate in the refrigerator hatch. Yes, this works but I know it's not correct.

Now the weird issue. With the ground not connected I get rapid flashing using turn signal. Not surprised. However, the transmission will hunt between overdrive and not overdrive. Once, I reconnect ground to the grounding plate in refrigerator hatch, all works perfect.

Thanks for any advice

Sorry, should be in electrical section

the transmission issue will not be with the moho wiring but with the a pcm ground, that may be grounding the tail lights

It sounds like one or more poor grounds is causing some back feeding through different circuits. I had some issues with grounds and found some ground busses heavily corroded. The main issue was the cable grounding the buss to the chassis was corroded so the power was feeding back through the other circuits. If the previous owner crossed the camper and chassis wiring you could be in for some unexpected suprises.