Now put those three pieces together and place it on the door so the screw holes in the door line up with the pegs (looking from the inside)
Screw the mirror on from the inside using the screws that should come with the mirror, not the bolts... they're too big:
Now, pay close attention to this part, lol. The connector that came with my mirrors had 4 pins in a square arangement... the oem connector has 4 pins in a row arangement. What I recommend doing is taking the piece you cut off of the old mirror, plugging it into the connector in the car, and stripping the ends of the four wires. Then plug them into the square connector ports, and turn on the car and test the power functionality. The colors were slightly different on my car, so I can't give you an exact color chart, but look at the picture and see if that helps. Place them into the square connector and test the power. If you have them in the wrong place, it just won't work... it won't hurt anything. Get them positioned correctly here though:
After they're positioned, connect them somehow. I saudered mine, but you could splice the wires and use butt connectors, or whatever method you have for securing these wires in their places. Here's my saudering, which worked perfectly:
After you're done, tuck the wires down into the door:
pop the face plate back on and you're done!
Enjoy your new M3 style mirrors!