Exactly --My guess is the coil power wire. From the factory they had no fuse in that circuit. Wire to the points often fell off and then the whole wire loom melted from the dead short. Common fix was too move the wire with a jumper to the other side of the fuse block. At least then when the wire came loose all it did was blow the fuse to the horn.
Fix the loose wire put in a new fuse, or wrap the old one with a gum wrapper, and keep driving.