Hi Tamas. You dont say what year your Focus is, but as a rule you will find it on the front of the gearbox, about half way down. That is to say on the passenger side facing front. It will have two wires going into a triangular plug. To test it, remove the plug, turn on the ignition, (dont start the engine) make sure the car is safe, hand brake on, even better, someone in the car able to apply the footbrake for your safety. get something like a piece of fuse wire or a paper clip and insert it into the plug. It may spark a little but won't give you a shock!! then check the reverse lights. if they are on then the switch is faulty and will require replacement, if they are not working, check your connection again at the plug to be sure.If they still dont work, a bit of investigation is in order, you may want to call an electrician. The switches are readily available at a Ford dealer, but be aware, they are made of aluminium and overtightening can snap it off!
Paul, January 2008