Dang, this is an old thread.
I tried installing the air horn twice in two separate attempts. Never could get it to work properly, the pump enough juice, the fittings, fabing a bracket, the hoses, clamps, zip ties, aiigh. First was actual horn type, then the Stebel following this thread. Still no success on the 2nd bike.
Finally ordered twin PIAA horn kit off Amazon (oddly enough by mistake), and works great. Really loud and leading all these bikes around and people pulling out in front us all the time, it gets a lot of use. I honk at every idiot in a car that comes near us.
Here's what I ended up doing: Maybe this will help something. I hated the stock beep beep horn.
PIAA Dual Horn Mod
After my two failed attempts at installing an air horn on the busa, finally relented and let's keep it simple.
This is PIAA's new twin horn kit.
Not a lot of room inside the nose, but here's where I ended up on the left side. A simple bolt through the air intake is all that's needed. Leave the old horn in place. (it's tough to take off & get back on)
Use some wire connectors and just plug them into the original stock plug after figuring out which is + & -.