The spring goes under the steering wheel, between the whell and the mast jacket bearing. it doesn't have anything to do with the horn, as the horn contact itself is spring loaded.
Here's a page from the '55 manual showing where the spring should sit.
Actually, it's funy this came up, got me thinking, so i pulled the wheel off mine just to look. Sure enough, I forgot to put that spring back in!
Now I just need to remember hware i put it!
