Having a broken mirror on your Ford Focus is not conducive to a good driving experience, but replacement at an auto shop is often expensive and time-consuming. Replacing the mirror, however, is fairly simple and much more cost-effective.
Removing the Interior Control Paneling
Roll down the window on the door on the side of the car that you want to remove the mirror from. Grab the control panelling--which is exactly opposite of where your mirror sits and has the mirror adjustment control switch on it--on the inside of the door where the window slides down into the door. Pull back toward the rear of the car. There are three clips that hold the panel in place and with a sturdy pull toward you and away from the door, you'll pop them loose and be able to remove the panelling. You may have to wiggle the panel up and down and back and forth slightly to pop it free from the third clip. No worries though, as the panel will pop back into place as easy as you remove it. The panelling is still held to the car by wires at this point.
Unhook the Wires
You'll see two wiring harnesses. According to MyFordFocus.com, one harness is for the mirror control and the other is for connecting the control to the power supply. These are held on by small clips. Pry the clips up with a flathead screwdriver and pull the harnesses connectors free. Set the panelling aside.
Unbolt and Unscrew the Mirror
Carefully remove the single bolt that holds the mirror in place by using a wrench and a 10mm socket. The bolt is found under a piece of foam that you can see once you remove the panelling. Patience is needed and care should be taken because if the bolt falls into the door you'll have to tear the panelling off to retrieve it. Once the bolt is removed, use a torx-head screwdriver to remove a single Torx-head screw and washer--again, be careful not to drop the screw into the door. Pull gently on the mirror to remove it. You may have to use a trim tool or a flathead screwdriver to pop the mirror free.
Replace the Mirror
Replace the mirror with a stock replacement mirror or aftermarket mirror and snap it into place on the outside of the car. Thread the bolt and the torx-head screw back into place and tighten. Lift the panelling and reconnect the wire harnesses and then snap the panelling back into place.