only one subwoofer on at a time?

[Robbie965]

I've installed two JBL GT5-12's connected to a JBL GT-1004 With a capacitor. My problem is that only one sub will work, no matter how I wire it. I can get both working if I connect my speaket wires into the same channel, but according to the spec sheet on this amp I can have 320W on 2 channels bridged. Help please? I've spent quite a long time trying to do it. Do i need to run more wires? Help would be appreciated on how to wire this thing. Pics will be coming soon.