Heres the situation.... The sound system in my cossie. All speakers changed to better ones. Ive got a 4 channel amp in the boot which is powering the bass box and the front door speakers.

Radio A works fine when im listening to the radio. I put the radio/cd player on the aux setting so i can listen to my phone or select cd. The amp doesnt power up.

There is no power to the amp from the back of the radio to the amp. It works fine on radio.

So i swap the radio/cd player over with another on (B) it works fine for a few days then does the same as the first head unit.

Put head unit A back in and it works fine on radio cd and aux. A few days later its back to normal. It will only power the amp up when im listing to the radio.

Ha ha what a carry on.