Okay, I checked and adjusted the coil air gap to 18-20 thousandths. I removed the speedo bulb socket from the speedometer. The speedo bulb was good, bright at idle, but no taillight. I removed the speedo bulb, and still no taillight. I revved the engine, and the speedo light blew, but no taillight. I changed the bulb, and stil no taillight. Wondering why the speedo bulb blew, I checked voltage at speedo bulb, with headlight on. At idle I had ~8 VAC but at half throttle it was 18-19 VAC. Is this way too high? Seems like it to me. Maybe headlight coil putting out too much? Now what?