I would go to the 12 volt
power distribution connection inside the trailer, usually on the inside front wall. There you will find the battery cable coming to the fuse panel. At a point before the fuse panel you should find a terminal that you can pick up power from. The input side of the disconnect switch is on. Connect and FUSE your wire there and run the wire out through the body following the umbilical cord wires. Once outside secure the wire along the frame with tie wraps as needed.
Preferably use #10 wire.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles