I am installing my Sony deck tonight and I noticed a second plug in the back of the wiring harness besides the main plug which gets adapted to deck. It has several less wires but is still substantial, anyone know what this is for?

 

If the plug is blue, then it is the CD changer/XM interface. This harness terminates in a plug in the trunk. This plug is not used for aftermarket head units.

Magnus

 

Thanks!