I can try but my knowledge is limited. Did your car come with an alarm. If not that may be the spot were it was supposed to go. I have a 98 V6 and I have a location in my trunk with wires and all but it was for an alarm upgrade. I actually purchased the Ford Alarm to plug in but no go so I ripped out my entire car and wired it the hard way

The parts guy from Ford told me these year mustangs came fully wired so all the shop had to do was add pieces if requested when the car was sold. Do you have a voltage meter,...check your voltage on your wires. The RCA cables: to check those get a small radio with RCA inputs. If no sound comes to the small radio your RCA cables either are not connected, goes to a non functioning amp somewhere in your car or belong to something else that could have been an option to your car. Also do you have a remote 'on' cable for the Amp. It turns the amp on when the ignition switch is on and off when you turn your car off. Hope this helps a little. Its a wire that goes from your radio to the amp. Personally, Just upgrade your stereo. Its probably faster.