The Vehicle wiring, stop - turn - tail lights
are totally independent from the inside living wiring.
The Vehicle wiring depends on a good ground (White Wire) from the tow vehicle to the camper.
If you have one of those carry around battery
packs, disconnect the plug from the tow vehicle and connect the neg to the white wire on the plug then the positive to each of the following, 1 at a time and go look to see if the corresponding light
is lit. (Turn Left, Turn Right, Tail or running light).