My horn was not working when I bought my 66. The horn beeped when the negative terminal was grounded at the horn. The horn ring was not making contact with the steering tube. This problem was solved by soldering a wire to the horn ring and feeding it through the steering shaft. The horn negative wire was removed from steering tube and connected to the new horn ring wire. I also found some resistance associated with the ground connection going through the steering box, the ground wire was removed from the steering box and connected directly to chassis ground.
Link to pics: http://public.fotki.com/WAYNEWANG/