It is possible that tightening the QR fixed a loose connection internal to the hub, but it is also possible it was just luck. Have you tried jiggling the wires at the light? It is more likely loose or broken there. It could be internal to the light itself too. What you need is an independent source, such as a borrowed wheel, and also using your wheel with a borrowed light. I have a similar setup with a Shimano 3N72 hub and the same light, and would be willing to do that if you'll come to Brooklyn since I see you are local. Is it a 700c or a 26" wheel? Mine is a 26 mtb wheel, but it may not matter.

Check your wiring for shorts too, including the taillight. I have a DVM that can check.

Reply here if interested and we can go on PM for more details.