Re: im new. how to install 4-CH amp?
You wire the 2nd amp just like the first one. Power, ground, RCA's, remote wire, and speakers. Power wire like the others said... either an additional 8 gage or use a 4 gage and split it to the 2 amps. Remote wire you can just tap into (jumper from the new amp to your old one).
For RCA connections you can use "Y" cables to split the rear RCA's into 2 sets and drive both amps. Or if your sub amp has preouts, you can run from there to the rear channel inputs on your 4 channel amp.
Since you're using the rear preouts of your HU to run both subs and full-range speakers, you'll have to make sure the HU is not set for sub-out mode or all you'll get from the rear speakers is bass. Gotta use the lowpass mode on the sub amp instead.
1999 Buick Park Ave Ultra
Head Unit: JVC KWHDR720
EQ: Audiocontrol EQL
Front Stage: Hybrid Audio Technologies Imagine 5.25 mids, Morel Maximo tweets
Sub Stage: Boston G3 10", 0.5 cu ft sealed
Amp: PPI Phantom 900.4
Rear Fill: Boston SE953 6X9's