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!
Yeah, the lights are above earth in a wiring sense. You've replaced the wire and whatever connectors, so that leaves the hub. If you have a multi meter you could check for continuity between the terminals and between the terminals and the hub body. It could either be an open circuit or a active wire thats grounded and ungrounds when the QR is tightened.