Radio/Navigation wiring diagram needed?

I am in the process of installing an aftermarket radio while keeping the navigation. I have the wiring harness for the radio, and everything turns on and works on the radio. The person who I bought the vehicle from must've cut a harness off one wire that I'm guessing goes to the back of the navigation system. It looks like it comes straight down from inside the dash, the wire starts out black, but then has a connector with an orange wire just hanging from it. No harness or connector at the end of the wire. On the back of the navigation there's three harness inputs, two of them are close together and bigger than the third one. Those two I have the harness and can be connected.
The third one is small and looks like that one only wire goes to that spot. I just don't know what the wire is or what it is used for, until I do, I can't buy the harness and finish putting my system back together.
Do you know what wire I'm talking about? I have JBL radio/navigation system with 8 speakers if I remember correctly.
Any help would be very appreciated, Thank you.