1992 400SE.
The radio works fine while in Key is in the ON position (vehicle off) or while idling, but as soon as you put it in gear, the speakers go mute. The radio is still illuminated and I can change stations, but no sound is comming through the speakers.

I have to restart the car to get it working again.

Before I owned the vehicle, some already removed the stock AMP and put in an aftermarket Pioneer. The wiring harness has been changed, and the charging voltage off the battery reads 14.4V while idling and 12.4V while off.

Any ideas??? Thanks,