Whats the xtra red wire for in the 2000 impala wiring harness....its not connected to the harness itself.....?

i've put in a few radios...but i know it has something to do with the computer...the harness is just like any other one i have saw but there is a extra red wire with it...its not even hooked into the harness itself! Its for a 2000 impala ( no onstar and not the jbl system ) If you could email me back with any help it would be apprectiated thanks jeremy bigballer9856@yahoo.com