Electronic regulators are regularly quite sturdy, except for the wrong polarization.

It is relative easy to change the polarization.


On a B-type dynamo, with engine running and wiring disconnected,  connect F to the polarity that is wanted, for a few seconds, dynamo chassis to the other pole.

The shown drawing will result in chassis minus..


A dynamos are a bit more complicated, with engine running and wiring disconnected, connect  F to chassis, and D to the wanted polarity for a few seconds. Other battery pole to chassis


With the wiring connected, the shown method can be used to get the dynamo "started", but it may result in blown bulbs, if not taking care (turn all lights off).