There are 3 different electrical systems in trailers: Tow wiring, 110 & 12 volt inside. They interact but are separate systems.1. The tow wiring operates the tail & clearance lights, trailer brakes (if electrical) and charges the battery. 2. 110 system is pretty straight forward but does require electrical knowledge to install. 3. 12 volt inside receives power from the tow charge wire and battery. A Ground from the frame is connected to all interior fixtures via a ground bracket.