The dangling black wire used to be attached beneath a mounting bolt of the left coil before the terminal end broke off. I overlooked it originally because it looked like just another washer under the bold head. Once I took the insulation off the end of the wire and saw what was missing - that helped.
The bad news is that the headlight still doesn't work, but that appears to be a bulb that died sometime after it was last ridden in 1986.