big three

Yo im new here, building a 2002 f 150  4.2 in to a spl bass truck with blowthrough cutting out the entire back going big 4th order so i bought a new alt its a irragi 320 amp had three wires coming out of it on its harness and my harness in truck had two wires i hooked it up with a buddy left one...

Okay, so I put a system in my fathers 99' Chevy Blazer LT for him (and me of course) and its been starting hard, and the lights dim when I have my DD slapping. So I am thinking it time for the big three. I need some help though! First I wasn't sure if I have to have a fuse between the alternator...

Whats the best wire to use for the big 3?

did the big three and upgraded all wiring from front to back tin 1/0 gauge. and put a 2400 kinetik in trunk instead of the deka. amps still cut off around 9.9vlts whats the problem here? do i need a ground from front battery to rear, i have the rear grounded to chassis with 1/0. I have the power...