I'm familiar with the old lights that had one wire, using the frame / ground as the other wire. That's pretty straightforward with incandescent lights, but becomes more troublesome when you use LED's, especially when it's not clear whether a given headlight or taillight has an internal bridge rectifier. Most modern lights seem to have an internal bridge rectifier, even if they have clearly labeled contacts (positive and ground, for example).

But as I mentioned, I've now built a new wheel, with a Shutter Precision hub, which came with a new plug. So far, no problems. Fingers crossed.

Had I known that hub was coming so soon, I probably would have held off on starting this thread. It wasn't supposed to get here until June!