This might be a stupid question - my rear view mirror has power running to it. What is it for - there arent any switches on it and nothing displays on the mirror.

 

What year do u have?

Alarm; auto dimmer; GPS; radio antenna; pre-wiring for satellite radio/navigation...
mine is for the alarm & nothing else.

Maybe mine has this, but my brother says the 2008s used that wiring also as an overload protection for the starter.

 

Ok: ground wiring; starter protection & the other accessories, like backup camera...

 

My guess is its an auto dimming mirror. Does the bottom center have two small squarish openings? This would be the sensor that reads light.