The lock cylinder on a Ford Focus door is part of an assembly within the door that includes the lock motor. If you need to rebuild the assembly with a new lock cylinder, you must get into the door itself and remove the assembly to remove the cylinder. Not only will this involve working with a lot of small parts, but the exact procedure can vary depending on the exact year of your Ford Focus.
Unplug the negative battery cable and remove the inner trim panel from the door.
Rotate the side impact bolster counterclockwise and detach it from its clips.
Disconnect the speaker from the door by removing its four screws and disconnecting the wiring as it becomes accessible.
Unclip the inner door release handle from the front and slide it out.
Peel back the weathershield; you may need to cut through the butyl strip with a knife or scraper. Make sure you don't damage the weathershield or the door panel.
Remove the outer lock cylinder bezel by undoing its retaining screw on the inside of the handle assembly then unclipping the bezel.
Loosen the screw for the exterior handle from the inside of the door--do not remove it--then slide back the handle and pull it out from the door. Unclip the handle seals from the door panel.
Disconnect the electrical connector for the door lock motor by releasing its retaining clip with a small screwdriver.
Remove the three bolts for the lock assembly at the door's rear edge; this will require a Torx wrench. Unclip the reinforcement bracket for the door lock/handle and manoeuvre the assembly out through the door's inner frame.
Unclip the trim from the back of the lock assembly's security shield and undo the securing screws to remove the shield from the door lock assembly.
Pry out the adjustment locking clip from the remote control rod with a screwdriver; measure the amount of thread on top of the rod before you do this as this is needed to adjust the linkage on installation. If you break the clip, you will need to replace it.
Unclip the outer cable from the housing, then turn the inner cable by a 1/4 turn and remove it from the door lock linkage.
Release the cylinder retaining tab by prying it out from the handle reinforcement bracket with a small screwdriver.
Insert the key into the lock cylinder, turn it so it engages then pull out the lock cylinder.
Align the grooves on the replacement lock cylinder with the grooves on the reinforcement plate.
Push the cylinder carefully into the handle until it engages with the retaining clip.
Reassemble the lock assembly and install it, along with the exterior handle and the door trim panel. All of this is done in reverse order of removal.
To remove the door trim panel, pry out the cover trim for the grab handle and the inner door handle cavity with a screwdriver, remove the screws from behind these panels, disconnect the wiring connector for the window operating switch, remove all of the screws around the trim panel's outer edge, pull the panel away from the door and rotate it upwards at the rear.