I have the Stebel Nautilus on my bike and Wendy's bike too. Ours are mounted under the seat where the air box used to be. Ours came with the Relay too. I shopped around and if memory serves I found the best price at Scoot Works. Harbor Freight sells the Bad Boy that seems to be the same horn.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!