I haven't looked yet so maybe you guys could tell me. Is there room under the seat on a 2010 Dyna to hide the horn?

 

I don't think there is enough room under the seat but here's what I did on my 2010 WG. I went to O'riley auto parts and bought a pancake horn for $14. I comes with a mounting bracket which with a little grinding and drilling will fit nicely bolted to the battery case in the lower embeded nut. Horn will sit behind rear cylinder about 1.25 inches. Removed the battery and ground off the 2-3 threads protruding from the hex head bolt. Then just added enough wiring to extend to oem connectors and works just fine. Hidden and still loud enough to work. Bought a disk brake insert medallion at the HD dealer and stuck it over the hole where the oem horn mounted. Will post pics tomorrow. Pretty simple, looks good and cheap to boot.

 

Lol...

 

+1 on that, you can just pull the horn wires back to the new position, they start under the seat.