Chevyman, The actual button unscrews from a contact plate, which is just under the button. The contact plate is held in place with a spring wire that wraps around the three pronges from the piece under the stearing wheel. After you take off the spring wire and the contact plate there is a nut that holds the stearing wheel on.

If you need some pictures of the horn assembly contact me directly and I'll email them to you.

Good Luck
George