Need Help With Amp Install

[jn24uk]

I am in the middle of installing an Alpine MRP 250 Four Channel amp with the Factory Head Unit, Bose and Onstar in my 2007 GMC Sierra NBS. I already installed infinity speakers in the doors.

The amp has speaker level inputs which I connected under the center console just outside the factory bose amp with the corresponding speaker colors that I found in the door when I installed the speakers. I ran the wires from the factory bose amp output to the speaker level input on the amp, then ran new speaker wire from the speaker output on the amp back to the splice point by the factory bose amp. The problem is after all of the connections were made I am only getting sound out of the front speakers. Bought the amp from Crutchfield and they said this location was fine to make the connections, that way I didn't need to run new wires to all four doors. I used a StreetWires OEM Interface Wire 9 Conductor Multi Cable. Not sure why the rear speakers won't work. Let me know if you can help, thanks.