Ford did a good job of hiding the ECM (electronic control module) on the Ford focus. Many Ford vehicles have the ECM mounted inside the engine bay, and some older models have the ECM mounted behind the kick panel, on the passenger side of the vehicle. With the Focus, Ford has found a new location: behind the glove box. Although you might think this sounds complicated to get to, it is actually fairly straightforward.
Open the glove box and empty it of all its contents.
Pull in on the sides of the glove box and pull the door all the way down -- there is a stop tab on each side of the glove box door; when you pull in on the sides, you neutralise the stop tabs and you can pull the glove box down, exposing the underside of the dash.
Look behind the glove box, to your right -- the ECM bolts to the inner bumper side. The ECM is silver, and has two large wiring harnesses connected to it.