Ok, I'm I hope I can get this question answered here. I have a truck with a 7-pin trailer wiring setup. I tow a horse trailer has lights in the sleeping and tack area. How can I install a battery so I don't run the truck batteries down while camping? I would eventually like to make it so the truck will charge the battery while I'm driving. But for now, I just need the install. Any info will help. TIA!