[antonye]

Check the voltage with a multimeter and you may also want to hook it up to an ammeter as well to measure the current draw. This will (probably) tell you if it's a duff circuit.

Have you tried adjust the alignment of the headlight using the (6mm?) allen bolt at the front? You may find this helps.

Also, try fitting some "brighter" bulbs in it. I put Halfords own-brand "blue" bulbs in mine and the light is definitely whiter and makes the beam more noticeable. I've heard good reports about their "20% Brighter" (or whatever %-age it is) own-brand range as well.