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Finicky, expensive headlight on Volvo XC90

I have been having intermittent issues with the driver’s side headlight. It will randomly fail for no reason while driving. This can often be remedied by turning the lights off and then back on again. The headlight will also fail not-so-randomly. Two triggers are driving on a bumpy road (we never get potholes in the winter in Ohio), and - here could be the clue to the problem - when I make sharp left-hand turns (90 degrees). What could cause the headlight to fail by making a left turn? The ballast has already been replaced once under warranty (which has since lapsed), and the dealer has wanted to replace the bulb since the xenon bulbs are quite expensive, and may not actually be the cause of the problem. I’m stumped, so I figured I’d turn to my last resort - you guys! Any insights?

It sounds like it’s either the ballast failing again, or the wiring to the ballast is loose or otherwise making poor contact somewhere. I doubt it is the bulb. Here are some things you can do to narrow down the problem.

  1. You could rule out the bulb by switching the left and right bulbs around. Be careful when handling the bulbs and wear gloves to prevent damage to the bulbs.
    After the bulb switch, if the problem stay on the left, then it’s not the bulb.

  2. You could rule out the ballast by switching the left and right ballasts. After switching, if the problem stays of the left, then it is the wiring and not the ballast. If it moves to the right, then the ballast is defective again.