Dynamo fuse?

[Bob Culver]

On the later cars the field fuse seems to protect only the field resistor. It is only in circuit on Summer charge. An intermittent connection beween cutout input, including the contacts,  and battery would cause the bulb to glow bright and likley blow a moderate rated field fuse if on Summer.  Rating is is not critical. With all ok  should still charge on winter without fuse (removal a convenient way of switching off dynamo on long day trips). All assumes your car is later wiring. Does the ign bulb still work?
The standard checks for dynamo operation covered recently and many times before.