Was the fuse blown in the first place? Maybe the horn is shorted and blowing fuses. If so, you need a new horn. Check to see if the new fuse is blown, if so disconnect it at the horn and put in a new fuse. Try the horn, which won't work because it's disconnected. If the fuse is still good, try reconnectinig the horn.
Try it, if it blows the fuse, the horn's bad and needs to be replaced.
If the fuse never blew at all, you'll have to trace power to the horn.
The horn system is not usually expensive tro work on.
If you want to find an Ford specialist or an auto electric shop here's a directory link for you: