Horn on my 72 just quit working.

Above is the post I meant. The "slip ring / brush" refers to the spring-loaded copper "horn contact roller" on the turn signal switch (white plastic in photos) which rolls on a copper ring on the underside of your steering wheel. If you ground that roller, the horn should sound. If not, the problem is in the wiring down the colum. Again, before removing the steering wheel, try grounding the black wire in the bottom column connector (body side). If that doesn't sound the horn, the problem is not in the steering column.

Finally, I just remembered a problem when my horn stopped working in my 65 Newport. The horn button was good and when I shorted the roller to ground, the horn worked. The problem was that the ground path was thru the steering rod and C-bodies have a rubber isolator in the engine bay so those elegant drivers aren't bothered by nasty road feel. The jumper wire across the isolator had broken. Shouldn't be a problem in A-bodies since should be metal-metal contact thru the steering coupler. The rod does float at the top end since the bearing is shrouded in rubber, at least in my 1965 Dart.