So I bought a z here a couple months ago and someone had completely gutted the rear speakers and put g35 seatz in the rear of the car. I'm attempting to fix the interior and I'm not sure as to what the blue/red and black wires are for. I think they are for speakers but I don't know which as I already know the plugs for left and right.

 

Are you saying you bought a Z with rear seats?
The colored wire goes to the "+" terminal, the black wire goes to "-". GL!