Yes, the horn contact buttons that are integral to the turn signal switch come in two flavors. Early '66 to '73/'74 style (2 contacts) and late '74 to '77 style (1 contact).
Since the back of the steering wheel is where the horn circuits do their business, the wheel much match the type of turn signal switch. The change from two contacts (no horn relay under the hood) to the single contact (using a horn relay) was a running change sometime near the beginning of the '74 model year. So there are some '74 steering wheels with the early styling, but with the single trace of the later model wheels.
For a smaller wheel with a slightly larger ring (but with the later styling unfortunately) you can find those from a full-size truck of the late seventies. Just be sure it's got either one, or two traces to be sure that it fits your vintage of turn signal switch and number of horn contact buttons. Full size trucks of the later seventies came in both flavors because some used horn relays and some did not.
I think the cure, or proof of concept would be if someone has a later model column, or Direct Fit tilt column, and tries to retrofit an early turn signal switch. There have been those that put the later switch in earlier columns successfully, so it seems likely it can work both ways.
If you manage to do that with the early switch and early steering wheel, you can simply reconfigure the wiring of the new switch to work with a relay. That's an easy thing and probably should be on everyone's list of things-to-do if they have an early style system.
A horn relay does all kinds of good things to the early circuits. Helps the contacts last longer, makes it more reliable as far as keeping the horn working even at lower voltages if something happens, and best of all makes for a louder horn!
It also frees up the switch from over-use if you choose to use dual tone horns, or an air-horn with compressor.
Paul
