BlatzKrieg

I have a 2004 Nissan Sentra SpecV with the Rockford Fosgate sound system. I went to install a new deck, but realized that there is a third connection of wires coming out of the factory deck, but all the wiring harnesses i found only had 2 connections. The other two sets of wires control the front/rear left/right speaker connections and the power/ignition/etc. connections. I did notice that when i connect up the two sets of wires that fit, everything works except the rear speakers are about 5-10% the volume of the front speakers, the factory sub seems to be fine though. There is a small factory amp in the trunk, with a bunch of wires coming out of it, but they are all bundled together in some black plastic insulation and I can't see where they are going/coming from.

If anybody knows what the extra set of wires does and how I can hook them up to my new deck so the rear speakers work properly it would be awesome.