I pass you a pdf link on the electrical wiring of the Focus, several models, I hope it works for you. If I find the electrical diagram I let you know.
https://josemaco.files.wordpress.com/2011/03/focus-dc-12-20051.pdf
Puff that good to find the fault. There is nothing more cumbersome than electrical problems in a car
I am sorry to disappoint your obvious answer but there is nothing short, the problem is that it has a bridged cable that is carrying more current than is due. I am tracking where it comes from and trying to see why they did it this way since I am not only having problems with the speedometer, but also with the central locking (which, when it reaches 10km closes, or should close the doors), apparently the Airbags as @celentauro says well and also something with the Gas team. They put a lot of hand.
Look, a short is when a cable is altered, hacked, or in contact with another. What causes overheating, malfunction, burning of rifles. I obviously did not mean badly.