It's not the cracked steering wheel. The contact is made via two springs attached to the rear of the steering wheel, which contact concentric circles of metal, insulated from each other. When you press the horn button, two contacts complete the circuit and the horns sound. I suspect your horn button is faulty.
I just had this happen to myself inthe last month. I have a Grant Steering wheel on the '67, and the spring that holds the upper contact plate was getting weak.
I actually had printed out some VMF postings from 2001 in 2001 (imagine that), and the quick fix is to add some foam to seperate the two disks. The perferred foam is the same foam used for the window sash / insulation. Grey, not very dense, and is very inexpensive.
I pulled off the upper disk, put 4 small pieces of the foam on the back, and re-installed. Probelm fixed.
After I typed all of that in, I hope it helps. It worked for my problem.