Me and a friend are installing an after-market pioneer radio in my 2004 Grand Prix GT. I honestly don't know what I am doing but he does, but we seem to have hit a speed bump. We have connected all of the wires from the stock stero except for these 3 that were wrapped seperately, brown, green and black, all with a white stripe on them. Anyone have any idea where they are supposed to be connected? My after market stereo has power, it was able to take in a cd and eject it, but the display was not on at all and i could not get it to play any sound...

im hopeing your friend used a wiring harness to install it and not just doing a hack job on the wires. you should be using 1 of 2 possible harnesses, 1 will just have a chime module built into it since the door chime comes through the stereo. the other 1 will allow you to use your onstar through it still and have the chime module.
sorry i cant help on what the wireing colors are supposed to be on the gp as i havent installed an aftermarket in my car yet. but i have installed an aftermarket stereo in my wifes 05 cavy which is setup the same -onstar it required the GMCO wiring harness.
if your friend already did the hack job on the wires your best bet would be to get a wiring diagram for the stereo wires. there may be 1 online somewheres or you can usually get a copy of it from your local dealership

umm I am pretty sure he is doing a hack job, and i looked online for a wiring diagram and couldn't find one. Thank you for the fast response though and if anyone else has some more information that would be great (i dont have onstar btw)

You could save yourself time and trouble if you had a wire harness check out http://www.crutchfield.com and you should be able to find everything you need.

Better yet you could save your radio and just pay the money to have someone who knows what they are doing install it.

he may not be able to go that route anymore since his wiring is now hacked up.
if your friend left enough line on the connector side i would really suggest connecting it all back together and going out and getting the GMCO wiring harness, its a little pricey at $100 but its the 1 you need.
if you get the harness you would have that stereo done and installed in about 10 minutes. the harnesses are idiot proof all you gotta do is match up the colors and plug it in

https://www.zzperformance.com/grand_prix/products1.php?id=796&catid=170

Check out this link my friend.