12-14. Most guys say 14 is fine. I just run 12 because I want to know I have large enough to carry the load. Also take your 2 wires and form a loop at battery end with enough slack to hook up. Then twist the wires together loosely to form a twisted pair. This will help reduce the chance of interference. You can also use a battery powered drill to twist them, but they don't need to be twisted tight.