What is the purple wire in the 2000 pontiac sunfire's radio wiring?

[deathnite20]

this wire was connected when the stock radio was in the car. When i changed out radios i had nothing to connect this extra wire to so i taped it and left it alone. but my problem is now my ETS, Brake, ABS, and Service Engine light are staying on now. So does the wire belong grounded somewhere or is there actually power coming out of the wire?
i also have a gray wire left over

 

[Blueberry]

try and find a wiring schematic.