Bicycle dynamo or light not working

The cause is usually a loose cable connection, poor earth contact, or a blown bulb (on older lighting systems). Check that the cables at the dynamo and headlight are firmly connected. Hub dynamos earth through the frame thread – lightly clean the contact surface with fine sandpaper. For LED systems with a USB battery, charge the battery and try the reset button. Sidewall dynamo: the friction roller must sit firmly against the tyre with no slipping. If the light flickers at higher speeds, the capacitor in the rear light is often faulty – an inexpensive replacement part available from specialist retailers. Do not ride in the dark without working lights – risk of a fine and accident!