I don't know about the wiring problem you have, except to say that you might try looking on the underside to see if the wires are run through conduit.
Battery wise though.. you say this is a new to you camper. Is the battery from the previous owner?
Start with the basics: you're going to need a voltmeter to play along.
1) With the battery disconnected from everything, "fully charged", it should have over 12 volts. If you don't have 12+ volts, you need to try charging it. You can do this yourself if you have a "trickle" charger, I have one for my motorcycles. Or you can take it to any automotive type store and they can charge / test it for you.
If the battery takes a charge and holds it fine, you might look into whether your tow vehicle is charging the battery. Hook it up, start your vehicle, check for voltage at the vehicle battery. Then check for a similar voltage at the camper battery. Recently my friend towed my camper.. he had no voltage on his 7 pin connector. Luckily I had the battery charged previously, so we just didn't hook it up till we got camping.
If the battery, after charging, cannot hold 12+ volts it's time to replace it.
1995 Toyota 4Runner SR5 4WD 5 spd
2002 Eagle Summit 12