[Spyderman]

Simon,

Remove the offending headlamp unit. Look inside the area where the black plastic headlamp mounting plate is, and find the headlamp harness where it passes through the plastic upright at the back of the headlamp mounting plate. There should be a yellow piece of plastic on the backside of the upright that slides up and down. Make sure you push the headlamp connector through the opening, and slide the yellow plastic piece up to secure the headlamp connector in place. As Tony suggested, you may want to place a nylon wire tie somewhere at the base of the yellow plastic clip to keep it in place. Sometimes these yellow plastic clips will vibrate loose and allow the headlamp connector to become lose and make you think that a bulb has burned out. When you're satisfied that the headlamp connector is secure to the upright, slide your headlamp unit back into place, and give it a firm push to make sure the connection is made, before locking the headlamp unit in place.

Hope this solves your problem.