I've been trying to troubleshoot this issue a little this afternoon. I don't believe the taillight coil is bad. Here's why.
1) When I first began having an issue, it was my headlight that wasn't working, NOT my tail light. I investigated and found that the speedometer light bulb tabs were bent, allowing the positive lead to touch the speedometer mounting bracket, grounding it out, thus direct grounding the headlight circuit. Important! The taillight was working at this time. I straightened the tabs, and the headlight came on as normal. Problem was, I no longer had a taillight. Thinking maybe I had a bulb with a loose filament, I bought two sets of brand new bulbs. New bulbs made no difference.
2) When I put a completely different stator assembly in, there was no difference.
Currently, I have all new working bulbs, and the original stator installed. Just for kicks I removed the speedo bulb, and touched the two wires together, and the taillight comes on, but headlight goes out. How come the taillight comes on when I short the headlight out?