When I purchased my '01 Sport my Jeep had the same problem with one of the sound bar speakers not working. Did some troubleshooting with the speaker wiring and discovered one of the speaker wires in the factory radio harness connector had pulled free from the harness connector in the back of the radio. Reinserted the loose wire into the harness connector which solved the problem.
Do some continuity tests with a VOM (multi meter) and you will find the problem.