I'm trying to find a wiring diagram for my 89' GL so I can install the radio myself instead of paying a 50$ fee just to get it put in. I'm simultaneously trying to learn more about my car as it is my first car and I wanna be able to work on it myself rather than relying on body shops, mechanics, etc. etc.. If anyone could help me out it'd be much appreciated since I'm basically a new born in terms of being in the car scene.

Search for a factory service manual. Ebay and online. There are some links in threads on this forum also. The fsm is far better and more complete than any of the generic books.

i can tell you now you are going to want to run a new set of wires to the front speakers.  You can run the wires just to the kickpanels and connect to the factory wires just before they go through the door pillar. (2 pole pink connectors....blue wires are the -neg )

 

this is because the factory setup uses a common ground between F/R speakers.  So you run new wire to teh fronts, and use the factory wires at the radio to connect to the rear speakers.

 

Don't have diagrahms to post, since Photobucket got lame.

 

but maybe I can look up some wire colors.  I will see what I can find in my FSMs

try 12v .com they have stereo wiring