jOe wrote:I didn’t notice much of a brightness change between 800-3000 rpm.
That's a pretty sure sign that the regulator is not doing its job. On mag bikes, usually the headlight is very dim, or flickers, or is dark at idle, but then becomes steady and bright at speed. If it's bright all the time, then the regulator is allowing too much generator output to the lights all the time.
6 volt Generators produce way more than 6 volts. It's the regulator's job to keep it in the (in this case) 6.5 to 6.8 range. How does the regulator do this? It does this by grounding the F terminal of the generator (inside the regulator) - open and close 50 to 200 times per second. When the F terminal is grounded, the generator outputs full output. When the F terminal is "open", the generator outputs nothing. So here's a quick check-> with the bike running, disconnect the wire attached to the F terminal of the regulator. The lights should go out. Hook the wire back up - the lights should come back on. If the lights DON'T go out, the field coils inside the generator may be shorted to ground.
But more likely is a regulator problem. Bike turned off. Remove the regulator cover (2 screws). With the wire connections pointed towards you, the unit on the right is the voltage regulator. There is a movable contact plate attached to a piece of spring steel. Push it up and down with your finger, and it should go up and down, making and breaking the contacts. When the bike is running, it opens and closes 50-200 times/second. After 60 years of this, the spring steel gets weak or breaks. If it gets weak, it may droop and hold the contacts closed all the time, and you get full output all the time. The result would be:
I didn’t notice much of a brightness change between 800-3000 rpm. If the spring steel plate breaks, you get zero output all the time.
Give those a try - no meter required. Hope this helps.
Dave