2011 GMC Sierra 2500 HD Denali

My USB port does not work on the truck. When I took the radio out of the truck, there is a mini USB male hanging out of the harness, but no plug in for the USB on the back of the radio. Is this not the radio/navy that came in it? Whoever owned it before me spliced into all sorts of wires and obviously had an aftermarket system. What should I do to get the USB working. Is there a wiring harness with the USB on it or am I just up the creek?