I don't know if this will help you much, btu we'll see. I have a 91 Explorer w/ the premium sound and had the exact same problem. on the aftermarket wiring harness there will be a blue "remote" wire. Hook that up to the remote wire on your stereo or to the power antenna wire on the stereo and it should work fine. What's happening is the stereo isn't turning the external amp(yes you have one) on.