I added Truck / Air horns to my 2013 LEAF but I did not replace the Horns used from the steering wheel. Those were upgraded years ago.
I wanted something louder, Something that's not exactly legal. So I can wake up people who are sleeping behind the wheel.
You can check out pics and descriptions here: http://www.salsleaf.com/truck_horns/index.htm
At the bottom of that page, I have links to Amazon that show the parts I bought and used in the install.