Right, use 12ga. wire from the plug back. And shrink tube your connections.
I was having problems with mine and made all 4 brakes into a loop with the wire so I could be 100% sure that all 4 were getting adequete power, and the same amount of power, at all times. However it didn't help much as it was more of a problem with the magnets in the drums not making good contact because of how they wear. I replaced the brakes and didn't replace the hubs. Takes a while for the magnets to seat good into the scoring inside the drums from the old magnets. If there's too much, or too deep of grooves on the magnet mating surface in the drums you have to replace the drums. Yeah it's a bum deal... Brake shop told me they can't mill the surface smooth where the magnets ride. I hate electric brakes...