I had been confounded by an intermittent fog light on my 01 X5. I checked the bulb which was OK, and the power to the connector was good. Each time I would remove the fog light and reinstall it would work for a few days and fail again. Not wanting to shell out $150 for a new light assembly I finally found the problem. The light depends on power getting to the bulb from the connector via metal flashing on a plastic assembly. My ohmmeter verified this was the problem. I removed the copper wire connector from the plastic flashing post and used the wire bail holding the bulb in place to make a direct contact with the copper wire connector. My favorite kind of fix, no parts, no money, no tools required.