Originally Posted by BUBBA
try hooking up a different speaker to the wires. maybe speaker is dead. my wifes speakers in the back of her jimmy didnt work when we got it. both speakers were fried.
Second that... I'd pull the door speakers and test them for continuity; they may be blown after all.
Actually before you disassemble anything, start the radio playing, slide the balance/fader controls to the driver'* side so you'll hear the problem speakers clearly if they come back to life (even momentarily), leave the driver'* door open, grab the wiring harness in the black accordion-pleated rubber housing where it jumps the gap from door pillar to door, and wiggle it and twist it however you can.
If the speakers cut in and out, that'* where the problem is. It'* the most likely spot since none of the wiring has to flex at all anywhere else. If so, the rubber flexy piece in the door jamb has plenty of room in it for more wires, so you can thread a couple of new ones through it and bypass the broken leads that way.
If that doesn't turn up anything wrong, start at the back of the radio, make sure it'* actually putting out a signal on that channel (do _not_ skip this step; rig up a spare speaker if necessary), then progressively work your way outwards towards the door until you find where the wiring goes dead.
My guess in order of likelihood here is:
1) Broken wire(*) in the door jamb
2) Bad connections at the stereo
3) Blown speaker(*)