If the bulb and socket are good (use a ohm meter) the check the ground from the screw part of the light bulb to the frame of the motor. Looks like a good restoration and the paint on the frame and shell may be creating a open and not shorted to create another electrical path. What I did to avoid this problem is to run another wire from the cast headlight to the frame of the motor. I also use small wire terminals to be held with the screws,
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