im no expert, but ive seen people use everything from thin to real fat wire. all depended on their needs. most of the time it was for stereo power upgrades. large systems.
but ive read here that it will make your windows move faster and the lights a bit brighter at idle. some claim a mpg increase too, not sure about that one tho.
ive looked into it myself and want to do it too, just haven gotten around to it yet.
if you google "the big 3" you'll find some gp's all wired up with some how to's as well.
