As everyone says, the most likely culprit is an earth.
To check, remove the headlamp and using a piece of wire clamp one end to the engine and turn on the lights.
Connect this wire to the earth terminal on the back of the headlamp .....
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The wiring dissapears up under the wing and can be accessed by removing the 'eyebrow' ..
Here's a pic of mine befire I remade everything ... that bunch of black wires is the earth which I think (can't remember) is terminated back up on the bulkhead.
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