When this happened to me years ago, I started at the horns with a VOM & a 12v source, and traced the wires all the way up to the horn button on the stalk.... and found the ground wire had cracked. It goes THROUGH the steel stalk and is soldered to the opposite side. A very hot soldering iron and simultaneously pushing the wire through the stalk rejoined the thing. The factory wire is a bit too short and is actually under tension while being soldered;I managed to pull a tiny bit more wire around the turn signal switch to relieve the tension.
