new one for me all these years never had it happen before! driving down the road in my wifes 72 dart and the horn starts blowing pull over pull horn button off of tuff wheel pull wire still blowing, go under hood pull horn wires to shut it up. have not had time yet to check it out, anyone else had this happen?going to try a spare relay if that does not do it it looks like time to trace wires.

over the years, i have had the horn wire on the turn signal switch break at the switch, then grounding on the internal column surface.
also, have had the spade plug in on the horn button come unplugged, causing the wire to ground on the wheel.
and, like you have said, the relay go bad.
i hope it's an easy fix for you.
please report back with what you find.

Mine had a burr on the horn ground plate in the steering wheel that pierced the plastic insulator and grounded to the column.

begging disconecting the turning switch plug down the column. If stops, then the black wire on turning switch harness is being grounded somehow. Wire itself or as mentioned the pushrod got broken and is grounding with column surface around.

Or steering will contact is loosed and being grounded around