Originally Posted by
Trevtassie
If tightening the QR did actually fix it, it may be a broken connection in the hub, the Shimano hubs have the "earth" connected to the bike chassis. So there may actually be a connection being made because a QR can measurably compress an axle (which is why you set wheel bearings with the QR done up). Alternately , it could be the "positive" (hah AC, but you know what I mean) contacting the chassis, and the QR pressure uncontacts it. Best way to test would be with a multi meter, during a fault time. The earth terminal should be connected to the axle with zero resistance, the other terminal should have some resistance between the other terminal and the axle.
Right, that's what I've been thinking (emphasis on your first word). What worries me, in this scenario, is: the lighting system, both headlight and taillight, "should be" electrically isolated from the frame/fork. The tighter QR may have made a better electrical connection between the axle and the fork, but if the lights are truly isolated, as they should be, this wouldn't matter... right?
By chance, USPS brought me a new hub today. So I'm busily building a new wheel that may perhaps solve the problem, assuming there's a problem in the hub.
More later. Thanks, all, for your suggestions so far!