You might also do well to check your external amp. I don't know you have one for a fact but if you follow the wires from the back of the radio to under the steering column, you should be able to find it. One other thing, I had a problem where one of my speakers slipped a little and the metal contacts ended up touching the door panel. This caused the amp to shut down to protect itself. Try taking the door panels off and testing them, especially if they are aftermarket speakers.