Anybody know what the top small square hole in the radio bezel is for?
Do you mean this one?
no, the little square hole near the top, in the bezel itself.
Ok, sorry, as soon as I posted that I was thinking the power button was just too obvious.
If it's where the arrow is pointing to then it is where the temperature sensor for the Electronic Automatic Temperature Control (EATC) is located if the car has that option.