Dear Norman,
Just to add to the excellent advice from Roger and Stan: If your dynamo has two terminals – one called POS and the other called F1 or just F, I believe that there is a strong possibility that no regulator should be anywhere in the system. The F-terminal connects to the field coils in the dynamo, and on my 1936 Squirrell a cable leads from the terminal up to the headlamp. The switch on the headlamp will direct a current from the battery through a resistance coil on the rear side of the switch to the field coils whenever the headlight is off, to avoid overcharging the battery. When lights are switched on, the field coils will receive much more current, to compensate for the electricity consumed.
On my 1938 Squirrell there is a current regulator, and no resistor in the headlamp.
I will therefore advice you to look inside the headlamp to see whether a resistor coil is mounted between terminals on the rear side of the switch.
I have a Lucas manual covering the magdyno from the period, and can copy it for you if needed.
As Roger indicates – if the armature of the magneto is damaged, it can be rewound and fitted with a new condenser. I have just had it done in the U.K. – it cost about £200.
I wish you the best of luck!
Kind regards,
