My 2000 grand am has to wiring connectors on back of radio? What is the 2nd connector for?

I have a 2000 model grand am gt. I am installing aftermarket radio in it. I have bought the correct dash kit and harness. The factory radio has an antenna wire, and 2 connectors on back. One with several wires and the other with not so many. Install harness does not have anywhere for other harness to plug in. What is that second harness for??