My dealer told me the cameras generally go up on one of the rear clearance lights (I would assume the center), I am waiting for clarification from Jayco if there is a mounting backer up there but have not heard back yet. The unit I have is prewired for a camera but didn't have any details in the manual on it.
As for the wires you are seeing, you are likely seeing one for the turn/brake light, one for the tail light, and one for either ground OR if your light has the clear reverse lights its for that and the ground is coming thru the trailer frame/sheet metal. You will want to wire the camera unit into the tail light circuit, you should be able to use a meter and determine which one has power with your vehicle running lights on.
Note also you will have to run with your lights on for the camera to work.
2016 Jayflight 29BHDS
2015 Ram 2500 Laramie Crew Cab - 6.4 Hemi
2013 Ford F150 Supercrew EcoBoost, MaxTow (Loved and Sold)
Equal-i-zer Weight distribution system