Mirror, Mirror on the windshield....
 

Question for the Guru's out there, just purchased a '11 LS Panel with ON STAR and was wondering I purchased a mirror, from a member here, that has ONSTAR, as well as compass, auto dimming, and a 4th button I have no clue on, I know the mirror will physically bolt up, but, will the compass work? Would it affect the ONSTAR?

As far as those buttons:
Compass on/off
Hands free calling
OnStar info
Emergency

But. All that info is in your owners manual. Along with how to calibrate the compass readout.
Check if the plug ends match up. Or if your car even has the wiring plug. It may plug in and work. Just might need the calibration.

Beat me to it George, so BQ, X2 to what he said.

Y'all will have to plug it in and see, it should work, I've got one I installed on my '07 and it works

I installed basically the same one on my '11 panel. Everything but the reading lights work. I guess the body computer has to be programmed for those to work.

It's the first time I've had a compass in the car, It's kind of neat.