13-08-2021, 11:45 AM
Because of the way the ignition light is wired it does allow a very small current through the dynamo, but that has nothing to do with getting the dynamo charging. It is the small amount of residual magnetism which does that. When the ignition lamp has failed the dynamo should still charge. If the bulb is sound with good connections it may be that the wire wound resistor around the holder has broken. If this proves to be the case I suggest soldering a direct connection across the terminations of the resistor and using the lowest wattage 12 volt bulb you can get (old fashioned panel light bulb) in place of the original 2.5 volt. This will glow adequately when you switch on, and go out the same as its predecessor when the dynamo starts to cahrge.