http://www.fordforums.com.au/showthr...highlight=horn
The horn and airbag is a complete unit. I replaced it myself, but needed a special tool. It is a security / airbag type allen key with a 5 or 6 point head (the non standard number!) which also has an indent / hole in it. There are 2 screws/bolts on either side of the steering column with covers / caps over them.
I bought a second hand complete unit (airbag / horn / centre) from my local Ford wrecker. Cost $50 18mths ago.
A mechanic will know how to do it, should take 15minutes. 5 minutes is the safety precaution of disconnecting battery. Apply brakes to remove any electrical energy stored.
If you do it yourself, just be careful with the cruise control and airbag/horn wires. Airbags are an explosive device!
Reason for replacement was horn coming on randomly. Did it a couple of times. Cause: Due to my AU being parked on the street the heat build up in the car eventually deteriorates the foam insulation between the contact points of the horn button.
_____