I bought a small marine battery box, a small car battery (no vent) and
some std cable connectors (see attached picture). It was something
like $75 for everything.
The way I'm thinking about hooking everything up is as follows:
Directly wire the winch to the trailer battery using the existing cables and
spade connectors. Easy.
Run a wire from the positive aux power (#4 black wire) to the trailer
power panel (below the front of the trailer) then to the battery.
Run a wire from the ground (#1 white wire) to the trailer power panel
(below the front of the trailer) then to the battery.
For the two wires above I would just match the existing gauge and
verify the amp (size of fuse - I believe 40amps).
I'm leaning towards this variation because it seems very simple and
you don't have to depend on your truck's power to light the interior
or run the winch. While towing the trailer battery would be getting
charged up. If the trailer battery dies, it will draw from the truck's
battery.
Does this solution fly? What if the trailer battery dies and the winch is getting powered by the truck's battery? Would that cause a problem?
Trailer Wiring Diagrams -
http://www.etrailer.com/faq-wiring.aspx
