If neither the headlight nor the rear light shine, this is usually not due to a faulty hub dynamo. In this case, it makes sense to carry out a systematic troubleshooting. To find out whether the hub dynamo is still delivering current, it is recommended to carry out a short-circuit test: When the wheel is spinning, the spade contacts are shorted with a screwdriver. The wheel then becomes more difficult to turn and brakes. When the short circuit is interrupted, small sparks appear.