I used 1/0 guage wire for my battery relocation but you should be able to get away with smaller wire. I think the kits out there come with 2 or 4 gauge wiring so they have to work. Just sand down a spot on the trunk for a ground and drill into it and bolt it down there.
1999 3.0L Cougar: 220fwhp and 200tq
2003 VW Passat W8 with 4 Motion AWD
http://www.cardomain.com/ride/300644
PM for intrest in 3L SVT Contours, 3L swaps into your current car, Prepped 3L engines, or anything 3L related.
