If the compartment previously had a bettery, I expect the wires might be the 115 VAC to the converter and other AC stuff, and/or the 12 volt set of wires for the generator starter, which probably has a switch located somewhere in the camper. You could get hurt if you are not carelful here! You would want to find the 12 volt wires, remove the switch since it would be a momentary switch and be worthless, and intall a spst, high current switch (suggest a push pull - Western Auto) and two auto reset breakers, about 40 amps or more each, both cheap about $10 each. Install switch in positive side wiring from new to old battery,and the breakers close to each battery on positive side (hot) wiring between the two batteries. You can get an 80 amp 125 VAC slide switch in a steel box at Lowes for $20-30, which is what I did to add a second battery (did not find the push pull switch source til later which is identical to what is in the Lance) Remove the switch (easy) and throw away the steel box, but keep the switch and install it near battery. Hook up the battery using large diameter wire 4-6 AWG, keeping runs short as possible (the existing wire might be small gauge if (probably) a starting relay for the generator was used. Any questions, send me a message.