could be the bulb an very likeley to be but..... it has two filaments and uses a 35/35w bosch bulb from standard it usually blows them one at a time unless there is a gas leak from the bulb,it could also be the earth wire that has fallen off of the bulb holder or that the bulb holder has just fell apart as they do that on speedfights.take the front panel off and have a look there is a connector block you can pull apart as the headlight comes off in the front panel.
adam bike doctor, December 2009
