I have rarely seen the wheel buttons go bad unless they're really dirty. Usually in a rig that gets wheeled offroad, the horn element fills up with mud and water and corrodes out. It will even look fine on the outside, but no longer work. I would use a test light like stated above or even a multi-meter. Hook the meter up to the horn wires and have someone hit the horn button and see if you have voltage getting to the horn. If so, you just need to replace the horn itself... All that the horn is to begin with is vibrating membrane, it's actually quite fragile. I usually end up adding cheap aftermarket dual trumpet air horns. For the same price as a replacement horn, I have one that's much louder and much more obnoxious! LOL!
