I have a 2005 645 (E63)
My problem is that about a month ago i had condensation in the drivers headlight. As you do i swapped bulb and ignitor on to the working side and they where fine! So i swapped back.
Next i dropped the bumper and swapped the control module (ballast) over and the fault switched sides. So now i kept the working ballast on the drivers side and the faulty ballast now on the passenger side ready to be replaced.
Ordered a new one, fitted the new ballast on the passenger side. Switch on and both headlights Work!!.....for about 10 minutes and then the drivers side fails! I can switch off and switch back on again and it works again for roughly 5 or 10 minutes. So i guess something is causing the Ballast to fail
Has any one else had a similar problem? im reluctant to carry on fault finding with a £60 part, only so many i can afford to go through. Any suggestions or previous experience will be appreciated.