2001 grand prix gtp help

I have a 01 gtp and want to put a after market radio in and have been told several different things... so can someone help me?? it does have bose and onstar. is there a special harness i need? someone told me its like 150 bucks

the only special harness you need is the one where you will still be able to operate your steering controls. other than that it takes the regular 15 buck harness. i personally used the cheap one cuz i like to hold my remote in my hand. so instead i paid 100 bucks for the custom in dash kit you can get from humount.com

No special harness needed.

The standard harness will likely not have a wire to turn on the amp. That's easy enough to do as it's typically on a seperate connector.

I'd suggest a box from Axxess to retain your steering wheel controls.