ppl are going to burn you over the cap!! but if you want to use it. You hook up a power wire from the batt to the + side of the cap, then you ground the - part of the cap to the chassi. then the + side another wire to the + of the amp and the - side of the cap to the - side of the amp. hope that helped.. GL
Meh i'd just ditch the cap. If it came with this big 3 setup as you say then I imagine its cheap anyways. I've read around here you actually lose performance by using a cap. If your running alot of watts rms you'd be better off having a second battery (say 1500+).
if you want, just get true 1/0g wire and do the big 3 upgrade and ditch the cap. if you are planning on running lots of power now or anytime soon. start by looking at a HO alt 1st.. then a 2nd battery if necessary..
start with Big 3 and a solid underhood batt, like an AGM battery, depending on the size alternator you have you may just want to add a second batt, if you have some tiny 60amp honda alt then do that first lol
just sell it on craiglist and some dude will roll up wangin some Boss subs and give you $100 for it