Thread: Everything you ever wanted to know about auto dimming rear view mirrors

Originally Posted by RareGMFan

Sorry I didn't see this post earlier. How do you know the auto-dimming isn't working? What method have you used to test it?

If headlights behind you are blinding you through the rear view, the auto-dimming probably isn't working...

Sorry - couldn't help it...

Originally Posted by RareGMFan

Sorry I didn't see this post earlier. How do you know the auto-dimming isn't working? What method have you used to test it?

I figured it out. Apparenetly the auto dimming mirror runs through the sunroof fuse. Since I don't have a sunroof, I didn't think to check it. I read about it online and found the fuse was bad. After I replaced it, it started working fine. Since that, I bougth a Gentex-177 auto dimming mirror with compass and switched it out. Now I can tell which direction I'm going.

Great info! Is there a How-To for converting the 3 pin wire of a 2000 GTP to the 16 pin harness of an On-Star mirror? Cant seem to find one. Thanks !

Yea I am looking for the same thing. I bet that once power goes into the mirror the compass and what not will light up. I bet that all those other pins were for all the on star crap. So try to rind power for the overhead lights, for the mirror and the signal wire to disable the auto dimm in reverse and you should be good. I however, cannot even get the plastic cover off without breaking it but I have a strong rear window tint so Im ok with it for now. Once I get some of these pokers out of the fire, rebuilding second vehicle and fixing GTP I will post back here. Let me know if you figure it out please.