If the Alarm is a standard fit Bravo one, then its behind the passengers side indicator on the wing. You will need to remove the wheel, the inner wheel arch liner to gain access.
Yes, I think big al is right. I had a similar problem & solved by my mechanic. The contacts sit on some rubber and when the rubber disintegrates, it touches the metal and shorts it, causing the honk to go off.
or, theres a coin gotten behind your airbag. trust me, it can happen
also, if your airbag has been taken out, and put back in with a small spring missing, your airbag/horn button will be loose. i had mine on for about an hour with a spring missing on my 1.4 a year or 2 back. Every time i turned right or went on a roundabout my horn started blasting at everyone, lol...
Buzz
The champion of the Bravo 1.4
Owner of the Bravo 1.8