As I drove home from work earlier this week my car stereo started a very loud screeching noise. There was a smell of melted wire insulation. I've checked the head unit in another car and it is ok. Checking the wires that I can see behind the head unit I can see no wire damage or bare wire. When I check the wiring going to the head unit, I find that if I just plug in the right RCA plug, I don't get the screeching but the sound is very faint. Plugging in the left RCA plug I get the screeching sound. The audio system includes an amplifier. I can see that it turns on with the rest of the system. Looking at the head unit wiring diagram and checking for grounds, I find that the head unit ground is grounded as it should be, but also the wire that is marked as going to the car's illumination signal. I disconnected the illumination line but the stereo response is the same. I'm looking for suggestions on how to find the problem. Thanks.
