BTW, if your only symptom is dull headlights for a few weeks (until the battery went flat/died) then your alternator is most likely ok, as a dead alternator and/or regulator would have left you stranded long ago.

Do you have halogen or xenon (HID) headlights?

I'll have a look over the wiring diagrams and see if I can identify a common earth or supply source that could be the source of your problem...

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)