Camper pigtail was cut off !!!

I’m not sure some of the above suggestions are helpful in figuring out the camper side of the wiring. My advice would be to figure out which wire is the ground first by using an ohm meter. It’s likely the larger white one. Then I’d take a fused 12V source and start touching +12 to the wires one by one. One will be the left turn, one for right turn and one for tail & marker lights at a minimum. The large red one probably connects to the camper battery to charge it, assuming there is one on board. If there is a battery on board, you can also use a meter or test light to see if the battery connects to the wires.

Alternatively, look for a wiring splicebox where there may be a chance to trace wire colors by also pulling a taillight out to access the wires.