I assume the real trouble is inside the radio and not the external wire harness. The short will be with the wiring to the light inside the radio. I can’t remember for certain what the standard wire color is used for the light, but it may be orange or orange/white.
One car for driving and another one just for parts. That’s what I call living in the lap of automobile luxury … 
Good for you OP for finding the source of that pesky electrical problem. Aftermarket audio system install problems are a pretty common complaint here.