Should just have to run wire from the positive on say right rear to the positive post on the subwoofer, and a negative on the left rear to the negative post on the subwoofer.
Edit, also make sure the nominal impedance on the subwoofer is 4ohms. Most 4 channel amps when bridged must see a 4ohm impedence or (numerically) higher
OK, I have too many wires hooked up then. I'll see if I can get two of them out of there.
The sub is a 4 ohms.

