I ran the Stebel Nautilus on my GT for many miles. It's a tight fit (I put mine under the right side fairing, as I had HID ballasts under the left side), but it worked well.
The upside is that it's loud. Dämn loud. No, even louder than that.
The downsides are that it's big, so fitting it up under the fairing panels is tight. It takes a lot of power, and requires a 30 amp dedicated circuit and relay. And there is a slight delay as the air pump spools up. But then, look out!
Some riders have instead gone with one (or even two) "conventional" style horns, just using a much better quality, and much louder, model. These fit in much easier, and can usually be run off the stock wiring without any mods.
The Hella Supertone and the Fiamm Freeway Blaster are popular choices, although there are many others.
Here is a review of aftermarket horns
by WebBikeWorld. Ignore their bitching about the Stebel failures. I've never and any issues with the Nautilus, and neither have the vast majority of riders. The rest of the article has pretty good info.
Just another option to consider.
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032
All lower 48 states plus Alaska on the K13GT in two weeks . . .
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