Well PAC was worthless in their reply, so I called the place I bought it from, tune-town in sandusky, OH. They said the gm21 is for '88 and up, while the gm21b is for '98 and up. It sure would have been nice if the gm21 was labeled '88-'97. Anyway, I got the gm21b and the volume is still way too low and also only the rear speakers work. Nice step backwards. I'm afraid I may have to bite the bullet and buy an amp.