no prob, I'll move it over to the e36 forum.
Since it's the windsheild mirror allow me to give a little more detail. On the stock e46 the voltage/power is run on two little electric lines embeded on the windshield itself which runs to the metal base on the mirror to power it. You will need to drill a small hole on the neck of the mirror and soldier a + and - wire to the tiny circuit board.. (VERY easy, believe me), and run that up to the roof. I have one on my car and it's a very clean install.. no one even notices there's a tiny wire going up. In your case, I would suggest wiring into the grey/red and brown wires for illuminating the sunroof switch, since it recieves constant power. If you don't have a sunroof switch, then you'll have to run it around the windsheild to your dashboard and tap it into another circuit of your choice.