hermesgrafix

This weekend I changed out my factory radio with an aftermarket radio. Everything seams to be pounding better, except the bass. But question n for you guys. There was a total of 3 plug ins to the back of the radio. One being the harness on the drivers side, passengers side outer was the plug for the antenna and one plug next to the antenna plug in. Looks like 2 or 3 wires Sam looking plug as the antenna except yellow. Anyone know what this connection is for? For the xm? For the steering controls? Possible amp? Just got me wondering because its not hooked up. Thanks