Hi. Fitted a touch screen GPS/DVD unit to my Evo. Unit used original harness and aerial, with a canbus adapter. Unit switches ok and functions but poor FM and no AM radio tuning. Have a feeling it's to do with not switching amplifier on. Tried original unit back I. And works perfectly. Original unit seems to use canbus for switching. Any idea how I can get new unit to do same. Any help much appreciated.

Apparently the unit doesn't switch amp on and I need to run wire . Can someone give me any more info please.