Stereo & Electronics - Head unit upgrade ?

I have a 99 z28 with stock monsoon head unit in it and i was wondering what the three connectors on the back do? there are 2 10 pin connectors that clip together and one sepreate connector. i was wondering what the seperate one does because if i get a new head unit and the wiring harness to go with it, it will only have the spot for the 2 connectors that go together. is it just useless and just leave it unplugged or do i have to wire it into the head unit also?? if so is it hard to do? i have wired many headunits up but have never seen a third connector. is it for the cd changer that i dont have but was wired anyway? pls help me out thanks...

The third connector is for the optional CD changer - the wiring harness is installed even if you don't have a changer. All of this and much more is in the Monsoon FAQ sticky at the top of the forum.