Got into my truck and found this thing hanging from the back of my inside mirror. I was able to clip it back in place. Apparently the clip on one side was broken. And why is there a push switch on it?

It's the square box behind the mirror.

 

Compass module

 

Correct. Compass module and a wire if you have chromographic mirror.

 

mine kept falling off too. gorilla glued it.

 

Yep. Same here. I think it has something to do with windshield replacements. I’ve had about 5 replacements over the years.

 

had mine replaced a couple times too. you may be on to something there. lol

 

So, does turn off the compass or the auto dimming of the mirror. I'm assuming that is what a chromographic mirror does. Not that I have seen any auto dimming of the mirror. In fact, the mirror is so dark all I see at night is headlights.