Tommychu

I've googled to no end on this, searched everywhere and beaten my head on my desk and while i've found a bunch of useful information i still don't have an answer to this question:
What's that top right (when looking at the unit itself) portion of the main connector, on the back of most of the newer GM radios? I know the connector in the middle is that delco 9pin acc bus, the top left is for power and the bottom is speaker output but that last unexplained plug is bugging me.
I'm thinking it's for one of those odd stock amps. At least I hope it is, because then maybe I can do some electronical messing around to adapt it to my aftermarket amp. it has a speaker strength input but i'd much rather deal with signal strength if I can.
I'd cut the BS and get another pioneer but all of my decks like dissapearing at around 3-4AM. I don't get that with stock stuff. And the one I have here I pulled from an on-fire that I sold a while back.

I know, tl;dr I'm a bit long winded. but any help would be appreciated.