I have a Ford fiesta silver on a 04 plate and the horn don't work ... It works when the alarm goes off but not when I press the steering wheel.... Any ideas?

It is a function of the BCM

Principles of Operation

The Battery Junction Box (BJB) supplies the switched and control voltage to the horn relay (part of the Body Control Module (BCM)). When the driver air bag module is pressed, the horn switch (which is integrated into the driver air bag module) is closed and ground is supplied to the BCM which is routed through the clockspring. The horn relay then energizes, sending voltage to the horn, enabling the horn to sound.

https://www.justanswer.com/ford/4a38i-2011-ford-fiesta-ford-fiesta-horn-steering-wheel-s-owner-s-manual.html

and

https://www.google.com/search?q=2005+ford+fiesta+%22horn+relay%22+location

...

Sounds like you have an issue with either the steering wheel or the clock spring. You need to find someone that is experienced with working on vehicle SRS systems as your air bag module will need to come out for diagnosing your problems.

It is located in the SJB - smart junction box an it is a non- serviceable part . soldered to the board inside . Where do you hear the clicking noise coming from ? The SJB is located behind the left side kick panel .
SECTION 413-06: Horn 2007 Edge/MKX Workshop Manual DESCRIPTION AND OPERATION Procedure revision date: 10/30/2006 Horn The horn system consists of the following components:

• Horn switches (part of the steering wheel)
• Clockspring
• Horn relay (part of the smart junction box [SJB])
• Horn

For removal and installation of the steering wheel, refer to Section 211-04 .
For removal and installation of the SJB, refer to Section 419-10 .
Principles of Operation
The smart junction box (SJB) supplies the control and switched voltage to the horn relay (part of the SJB). When the horn switches (part of the steering wheel) are pressed, ground is supplied through the clockspring to the horn relay. The horn relay is then energized directing voltage to the horn and enabling the horn to sound. When the vehicle security system is armed, the SJB provides a momentary ground to the horn relay control side to indicate the system is armed, and an on and off ground when an intrusion is detected or the panic alarm is activated.
If your horns are not working ,you have a wiring problem or the clock spring is open . If the relay is bad the whole SJB has to be replace an the dealer would have to do that . Needs to be programmed ,with factory tool .
Symptom Chart Condition Possible Sources Action

• The horn is inoperative

• Fuse
• Circuitry
• Horn
• Clockspring
• Steering wheel switch harness
• Horn switches (part of the steering wheel)
• Smart junction box (SJB)

• Go To Pinpoint Test A .

You

If the alarm horn is the same unit used as the car horn then your problem is the contacts for when the horn is pressed. Some horns are activated by pressing the large center area of the steering wheel others have little buttons on the left and right side of the steering wheel. If the latter is the case make sure you try both pressure buttons to see if horn will work. Either way the contacts have to be cleaned or the wheel needs to be adjusted to allow the contacts to touch each other when pressed. That's most likely your problem.

You have 2 point of contact one is the alarm and the other is the horn switch itself, the horn switch is non op,

I don't have a diagram, but if I understand what you're saying, there is a copper ring at the top of the steering column, visible before you install the steering wheel. The copper pin is connected to the horn button. The intent being that when you press the horn button, it completes the ground from the steering wheel through the horn button, through the pin, to the copper ring.
If this is correct, there should be no contact between the steering wheel and the copper ring other than the pin. Check to see if there may have been a spacer (washer, etc) below the steering wheel on the steering shaft that holds it just far enough away from the copper ring so that only the copper pin makes contact.

THE AIRBAG AND HORN PAD IN THE STEERING WHEEL HAS TO BE REPLACED.THE HORN PAD MADE IN THE AIRBAG IN THE STEERING WHEEL.

If the alarm makes the horn work, then it is not the relay.
It is the horn contact or slip ring.
You need to take the cover off the steering wheel center.
But this could be dangerous due to air bags.
Disconnect battery first.
Steering wheel might have to come off.
Recommend a shop because most people don't have the tools for pulling steering wheel.

Are you speaking of the horn? Or the horn relay? Or the horn button? Or the horn button split ring armature? To remove the horn assembly in the steering wheel you will need a steering wheel puller and a U shaped clamp that will screw down to the steering bolt you will need a 3/4 socket with a 3-inch extension and a ratchet. You will also need to picks to pull center snap ring off to get to the parts under the plate for the horn. To remove you will need to buy 2 security nuts tork wrenches #8 I believe, you will have to disconnect the battery before working on it as the bag could explode if you do not have the battery disconnected. After removing the positive side of battery cable wait 5 minutes before proceeding. Then remove the two bolts that hold the front horn assembly and air bag from the rear of the steering wheel next remove horn air bag assembly and disconnect the wire for the air bag. Place horn to the side then remove the 3/4 bolt out from the center, next install steering wheel puller on the steering wheel and put in three bolts and tighten them evenly so that the puller is on straight. Screw center bolt into the steering bolt until the wheel comes loose, remove steering wheel and place it at the side, next use the U shaped clamp to press the center plate down 1/4 inch to be able to clear the snap ring around the steering wheel. With one pick hold the ring in place with the other force it between the steering wheel bolt and work the ring up and out of the grove it sits in. Next work it all the way up till you have it in your hand, and do not lose. Now pull plastic plate off if you put the wheels straight then it will go on the same way you pulled it off because it's keyed mark it with a felt tip pen so you don’t have to hassle with keying it in again. Next remove the plate and there you will find the horn contacts and the round disk that the connectors push against, so if you need more info just ask on this post.

its most probably the clock spring which you need to take the steering wheel off to fit