I used a similar horn, mounting location and system, and relay on my '12 XCT for about two years before Paul made his excellent video (see link in VJ's post above). I used Paul's video for the instructions on adding the diode, though, which I did shortly after he put that up. I have nine (still) pics and captions that describe the process in my gallery, starting at this pic:
All of these dual air horns are plenty loud, and the fairing has enough openings that the sound is not noticeably diminished. As long as you use a relay, keep the horn protected from the weather (which inside-the-fairing mounting takes care of) or at least have the trumpets facing down (to drain any moisture), and use beefy wire (16- or 14-gauge), you'll be fine with any of them.
"Living life is a great idea, but riding a motorcycle actually gives you a tool to do it..." -me
2013 Sunset Red Cross Country
Vic Tri-Oval Mufflers, Lloydz VM1-DR cams, AF, PC-V @112hp/113tq
Corbin Dual Tour seat, Klock Werks Klip Hanger bars, Vicwapz
Avon Contour grips, Kuryakyn Kinetic boards and rear SwingWings
Victory black LED headlight and Touring Pack, Madstad 9" windshield
This is the horn I have and I LOVE it! Screaming Banshee - Loud Motorcycle Horns and Safety Systems
The fact that I can still tap the horn button and get a polite beep (when the light changes and someone is busy texting), or hold it for a LOUD blast. The headlight flasher is just a bonus.
I went for the Stebel, via eBay,
got it mailed from local Geebung for $47 Aust incl. a relay and postage!
Cant go past that and its saved me from lane mergers a couple of times already, and its a real wake up call for txters in front of you wheb the light goes green and theyre just finishing thier latest txt!