Hello. Ive got a '91 firebird that i recently purchased. I just went to install a stereo in it and i swear this guy just took a hacksaw to the wires in there. Its a mess. I was wondering how to wire my stereo up since i have no idea whats what anymore. Any help is appreciated.

Don't know what you have to put in there but if you are buying, I always go to Crutchfield. After you buy from them, they give you lifetime tech support and will email wiring diagrams specific to your vehicle. I did this with my Corvette as I was changing from the Delco Bose to Alpine. I did it with my Jeep changing from Infinity to Alpine...their support is awesome and they are super friendly, polite and have great equipment at great prices. I also but my home entertainment equipment from them. They helped me setup smart harness use for the Vette.

http://www.iroczone.com/images/wiring/1992wiringb.gif ... see if that could help a bit

If the plug is missing, or been hacked too bad, you can use these:
http://www.ebay.com/itm/CHEVY-OEM-STOCK-Radio-WIRE-HARNESS-PLUG-1988-2005-/110703596756?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1991%7CModel%3ACamaro&hash=item19c672d4d4&vxp=mtr
http://www.ebay.com/itm/GM-CAR-STEREO-CD-PLAYER-WIRING-HARNESS-WIRE-AFTERMARKET-RADIO-INSTALL-PLUG-/331034636454?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1991%7CModel%3ACamaro&hash=item4d1333b0a6&vxp=mtr

Awesome. Thanks guys. I will try all this and keep you posted

Most yards will carry those 3 plugs (blue, white, black) that are needed to use with the Metra aftermarket adapter for our cars. I got a set for 10 bucks at a yard and soldered them back in.

The blue/white/black plugs are for older cars, such as my 87. It looks like the plugs changed in 88, if you believe the EBay ad.

You could just take off the dash pad and covers over the rear speakers and see what wire goes to what. You could use what you have and use some quick disconnect stake on male and female connectors. Wireing up a radio is pretty straightforward and Im sure you can handle it. I could not get the right connectors to plug into the factory harness so I just hard wired mine in. Just be sure to not mix up which terminal wire is positive or negative. You can test this by using a 9 volt battery and attaching each end of the wire from the speaker to it. If the speaker cone moves in then the polarity is correct, if the cone moves out the polarity is wrong. Just food for thought hard wireing can look decent if done right. Although if you can find an adapter for ease of use I would say buy it.

This is what worked for me.
http://www.ebay.com/itm/Factory-Radio-OEM-Reverse-Male-Wire-Wiring-Harness-11-/360880164525?pt=Motors_Car_Truck_Parts_Accessories&hash=item5406224ead&vxp=mtrand the attached wiring diagram

My '88 has these plugs. I'm almost positive GM used this setup into the early 90's.