[mrlmd1]

Either that or a Stebel air horn which you can buy for ~$30, and Harbor Freight has the same horn under a different brand name. I have seen the Framm in an Autozone store for $20. They both draw about 15-20 amps so you have to wire a relay directly from the battery (with an inline fuse) and you switch on and off the relay (and air horn) with the old horn wires from the handlebar switch. The original wiring to the horn cannot handle the current needed to operate an air horn and may heat up and burn.
The air horn and relay are in the same package with all the instructions and it's pretty easy if you can read.