Try some of these threads and contacts. Occurs frequently in these old trucks. Likely ground or dirt/corrosion in the column. Could be relay.
I thought I had the sequence of bits and pieces in my notes but cant seem to put my hands on them. Let us know if these techniques lead to something. If not I could dig deeper.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1115899/1.html

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1007850/1.html

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/969900/Re:_Hot_horn_relay.html#Post969900


~ HB
1966 Chevrolet K-10 | Ghost: formerly Flappy Fenders | In the Stovebolt Gallery
1962 Chevrolet C10
1962 Suburban