Radio electrical problem

[malibupaul]

This is a new post for a continuing problem. My radio, screen, and HVAC such as fan and indicator lights go on and off. Speakers crackle. The dealer and Chevrolet can’t figure it out. They changed the alternator and radio/HVAC control panel with no success. They now suggest replacing the radio. Here is the issue. When I have the ignition on such as the accessory mode, but the engine not running, all works without any problems, including the radio. Anyone familiar with the wiring diagram to comment what the problem could be other than the radio?

[gtstorey]

Have you changed spark plugs/wires/coils before this started with something of questionable quality or supplier?