1995 suburban facroty amp problem

I just bought a 1995 suburban.  Installed a Kenwood reciever and poineer speakers in rear doors.  The rear door speakers were not working when I bought the car and still were not working after I installed the new stereo.  I have checked and double checked to make sure the amp power wire (blue on harness) is connected and it is.  I am fairly sure that the amp is shot.  Is there an easy way to bypass the amp?  Taking a close look at the harness on the amplifier it looks like the rear speaker wires from the factory stereo are the inputs for the amp and the rear door speaker wires come out of the same harness.  The potential problem I see is that the speaker wires in the doors have a color in common, which usually means that they share a ground.  I would like to connect these speakers directly into my reciever without having to run speaker wire to the doors.   Any advice?

it you can clearly see the speaker cone, there is a trick you can do.  from the amp disconnect/cut the speakerwires.  get a AA battery, and strip the ends of the wires.  Seperate the wires from each speaker (there will be 2 for each) and hold one end of the wire to the - and touch the other one to the +.  you will hear a click/crackle.  It the speaker cone moves outwards, it is correct, If it moves inwards it is reversed.

I'd be surprised to see common ground speaker wiring in a 1995, but you could also use a multi-meter and check for continuity on the wires that are the same color.