I just got done with the last little bit of wiring, and my moped now has air horns. realllly loud.
I mounted them on the front fork, pointing down, and even gave them a coat of paint, because the bright red was a little too cartooney. I used a 4.5Ah 12v gel-cel and bungied it to the handlebars in a cloth lunch bag.
The pump is mounted under the side cover, and totally out of the way.
I'll post some pictures, once I get the digital camera again.