Alrite...well its prolly the wiring somewere, since another speaker doesnt work and the radio plays all 4 speakers fine in another truck. It is kinda hard to help ya alot with not messing with the wiring personally. I will try to find a diagram and look at my friends truck and see wat I can find. The infinity systems in these trucks are a real pita to work with. If you could take pics of the connectors that would help. In all honesty it would be 343243 times better if I could look at the truck myself..You dont happen to live in Illinois do you???