Running Lights Won't Work - Wiring Help Needed Please

OK I'm going to focus on a possible grounding issue. I sat down with the previous owner this morning and he said he had issues with the lights back feeding into his truck to where it turned on his reverse lights on the truck when he turned the marker lights on.

So he replaced the Lance plug in with a common 7 way and still had the reverse light issue until he played with the wires in the battery box of the camper.

Thanks for everyone's help it's appreciated.