i haave a 2004 Silverado it has all the bells and whistles, i bought it used so i just got it, on the rearview mirror, to the right of the red cross, there is a red light that comes on sometimes, and other times it is off. today it was off. the dealer doesnt seem to know what the light means, so maybe someone here has seen it before and knows what it is. the mirror has auto dim,and outside temp, and Onstar also.

thank you for the help

 

Greetings Terry welcome to the Forum.
Got an 03, but, I've never seen that on mine. Maybe it's related to your OnStar, you might call them and ask of no one has an answer here.