Check my "signature" for my links and answers concerning my install...
My vehicle used the gmos-04 wire harness initially. I scrapped it because it was stupid. I ended up getting a $30 harness I found at a local audio shop instead since I didn't need all the features of the gmos-04. There's a schematic that breaks down the wire harness into function for you. It should come with the harness you purchase. Crutchfield will supply it with your purchase too. Or you can go to places like the12volt.com and see if any installers have posted one for our vehicle.
EDIT: The first link won't show you pictures from my initial install so scroll to the bottom and see my update. You can see my original install in the second link.
