The horns are located in the passenger fender well in front on the front tire.
There are 2: a high pitched and a low pitched horn.
It is very common for one or the other to get "tired" and stop working.
You will need to remove the splash guard in front of the passenger tire to gain access to them.
Removal and install is very easy, they held on a bracket by one nut on each horn.
I have OEM replacements for $13.39 each.
Hope that helps,
David Roberts
928 SPECIALISTS
see Also http://sis125.berkeley.edu/928/horn.html