2012 Owners manual page 110:
Automatic Dimming Mirror — If Equipped
This mirror automatically adjusts for headlight glare
from vehicles behind you. You can turn the feature on or
off by pressing the button at the base of the mirror.Alight
in the button will illuminate to indicate when the dimming
feature is activated.
But the mirror on my 2012 Laredo X does not look like the one in the manual, and the on/off indictor light is separate from and adjacent to the button. A few pictures - left is on/green light, right is off/no light. The photo sensor for the dimmer is the small square to the right of the button. I believe Limited & Overland models with the rain-sensing wipers have a different mirror because the rain sensor is in the mirror mounting assembly. Which might explain why some have a different on/off/lighted button.