Electric Trailer Winch
See photos for ideas.
Most of the newer winches come with a wiring harness that can easily be wired into the tow vehicle. The previous owner might have gotten one with the winch and installed it on his/her tow vehicle. The best bet would be to see if a wiring harness is available for the make/model of the winch. If one cannot be acquired there are three options: 1) Run wires specifically designated for the winch from the vehicle. You need to have a dedicated circuit for this. Tapping into something that currently exists could cause headaches down the road. 2) Carry a battery in the back of the tow vehicle like he is doing now. 3) Mount a battery box on the trailer and place the battery there.