Just run the wires to a sensitive portion of your body, and when you push the horn button you will scream. It's likely to be at least as loud as the cheap horns Harley installs.
OK, so much for the cheesy attempt at humor. You can probably get a replacement on the internet cheaper than what your dealer would charge. And if the bike is still in warranty, it's probably not worth a 180 mile round trip to get it covered under warranty. If all you need is a basic horn to pass state inspection, go to Pep Boys or most other auto parts stores and look for the FIAMM Freeway Blaster. You can usually find one for about $20 or less and it fit's under the cover just like the stocker.
Jerry