1975 SIX PAC camper. I think the previous owner had issues. Combine that with my inexperience and I have some questions. I see no D.C. wiring plug or wires that look to connect to truck or seperate...
Yes you are correct there should be 2 different 12v one for your breaks/turn signals, reverse and running lights and second the interior lights and all other stuff running on 12v inside the TC that runs off of a converter/inverter inside the camper
If you truck lights are not obstructed by the camper then there may not need the break/turn signal
Seeing that I was only 14 in 1975 I'm not up on the technology at that time