Okay the best I can figure the GMRC stands for GM receiver and the GMOS stands for GM onstar. The ribbon cable has to have that kind of harness. It is the only one that will work proper. You don not have to run new power or speaker connection. Crutchfield told me I would but then I just made a call to metra and they hooked me up.
The GMOS-05 is prolly for the onstar systems but the GMRC is for the plain ol cd player, tape deck combo, or just the tape deck. Just be warned it is a tight fit and make sure to get the proper install kit. Go to a qualified audio shop and get that, don't do like I did and settle for wal-mart. You'll be sadly disappointed with the fit and finish, I am going to redo my dash install.
Adding a aftermarket head unit really seems to make the amplified speakers come to life.
02 Se with a few mods,
Coming Soon 1.9'* OR pushrods and other stuff