You have a PM

 

Does it plug in to something through the headliner for power?

 

These mirrors usually come with a harness that has three wires. 1 for constant power so you can open the garage with the car off, 1 for acc so that the autodimming function can activate when the car is turned on, and 1 ground. The oem style ones also have a 4th wire so that the autodimming feature turns on/off when you put the car in reverse (keeps glare down).

You will likely find constant +12v power under the headliner in the form of the cabin lights and ground, but not ACC. Most people route the harness down through the A-pillar to the fuse box where all three of these sources are available.

 

The harness was long enough to route to the fuse panel under the dash.