Horn does not work

Ford was the first manufacturer to get seriously carried away with the unnecessary use of complicated computers, and the horn is the most talked-about and troublesome circuit. In the past, the horn switch on the steering wheel turned on the ten-dollar horn relay which turned on the pair of horns. Today, the horn switch sends a digital or voltage signal to the most "intelligent" computer on the car, the instrument cluster. The cluster interprets that signal as the "horn request" signal, then sends another digital signal to the "FEM", (front electronic module), which sends current to the horns. Two computers involved in blowing the horn.

There are still two simple things that can cause a horn failure. One is a shorted horn, either the high-note or the low-note. If either one is shorted, the horn fuse will blow, then neither horn will work. Check the horn fuse, and if it is blown, you are in luck. Replace the shorted horn and the blown fuse.

All switches on the steering wheel go through a "clock spring" which is a wound-up ribbon cable in a plastic housing under the steering wheel. That cable will eventually break and cause some or all of the switches to stop working. The clue here is that will not cause just the horn to stop working. The "airbag" warning light will be on, and other functions will not work. Replacing a clock spring is a more expensive repair, and can happen on any brand of car.

The way your mechanic will approach this is to connect a scanner that can access the instrument cluster, then he will watch to see if it is receiving and recognizing the horn request signal when the horn switch is pressed. Next, he will access the FEM to see if it is receiving that request and if it is commanding the horn circuit "on". If the FEM is trying to turn the horn on, the last step is to measure the voltage going to the horns. If that is missing and the fuse is not blown, the driver circuit in the FEM is out. If either computer needs to be replaced, it will have to be programmed to your car before it will work. Often that can only be done by the dealer.