Just found this on a jbody forum, says you will just lose door chimes
If you have a pre-2000 car.. this doesn't apply to you
If you have a 2000+ J-Body then your factory head unit/radio/cd player/stereo/whatever is a CLASS 2 unit. Class 2 radios are wired differently than anything most stereo installers have dealt with.. and there's a LOT of misinformation out there about them.
Here's EVERYTHING you should need to know about them:
1. If you remove the factory radio from the car.. you will lose your factory door chimes and OnStar (if you even have it). That's it! Proof.. from YOUR owners manual:
(Thanks VaBeachKevin!)
Removing the factory deck will NOT affect your airbags (it's a separate circuit entirely!), your DRLs (also separate), your cruise control (again, separate), your oil change light (you don't even have one!), your *** life (well, maybe)...
If anyone tells you otherwise.. THEY ARE WRONG! (Feel free to tell them this. Better yet... let me tell them this!)
2. If you WANT to keep your factory door chimes and/or OnStar... you need to either relocate the factory deck using a T-harness or replace the factory deck with a new module for the chimes and OnStar speaker.
3. If you don't give a crap about factory chimes.. you can buy a $15 harness and hook it up using that! You don't have to spend $100 or more on a T-harness and relocate the factory deck. Your airbags WILL still work.
Of course.. you'll also need a deck mounting kit.. and a GM antenna adapter.. and whatever harness you choose that you need.
Want to know more? Go to my web page!
http://members.shaw.ca/johnz24/howto/2kaudio.html
I hope that helps some of you.. remember, don't believe everything you read... there's a LOT of misinformation out there