the thread in the VTX forum prompted me to post my install info for my Stebel Nautilus air horn on my 07 Boulevard S50.
I mounted mine on the left side below the radiator.
Wiring:
It comes with a relay so all you need is wire (16-18 awg) and a soldering iron. I mounted mine using hose clamps (3" diameter)
From the horn you run the -ve terminal to the -ve terminal in the fuse box - I ran the wire under the bike.
The +ve terminal of the horn goes to the relay terminal 87
I placed the relay where the stock horn was located and plugged the stock horn cables directly into the relay. I had black (+ve from horn switch) and black with a green tracer (gnd)
The black plugged into 86
The black w/green tracer plugged into 85
For Terminal 30 from the relay I ran it under the tank and seat to the +ve terminal in the fuse box.
The horn is super loud and you can listen to sound clips on their website.
STEBEL S.p.a.
I mounted mine on the left side below the radiator.

Wiring:
It comes with a relay so all you need is wire (16-18 awg) and a soldering iron. I mounted mine using hose clamps (3" diameter)
From the horn you run the -ve terminal to the -ve terminal in the fuse box - I ran the wire under the bike.
The +ve terminal of the horn goes to the relay terminal 87
I placed the relay where the stock horn was located and plugged the stock horn cables directly into the relay. I had black (+ve from horn switch) and black with a green tracer (gnd)
The black plugged into 86
The black w/green tracer plugged into 85
For Terminal 30 from the relay I ran it under the tank and seat to the +ve terminal in the fuse box.
The horn is super loud and you can listen to sound clips on their website.
STEBEL S.p.a.