A weird issue. My pass. side headlight will periodically go out and of course, that triggers the dashboard warning. If I move the switch from the 'normal driving' 1 o'clock position to the upright 12 o'clock position and then immediately back to the 1 o'clock position the headlight will come back on. Usually for just a few minutes until it goes out again and I must repeat the "fix". Usually after a few of these, the light will often remain on for the duration of the drive. I've consulted the manual looking for a possible faulty relay or something, but I'm having a hard time even determining if there is a relay to replace. The bulb is good as I tried replacing, does the same thing with either bulb. It's an '07 S80 V8. Any help in what to try or where to look is much appreciated.

 

Take a diligent look at the headlight bulb sockets. The heat damages them over time.

 

Found the solution . . . the ballast. Makes sense as the symptoms were similar to when a household florescent ballast begins to fail. I sourced mine through ebay. Takes just minutes to replace as the ballast is located on the bottom of the headlight unit.

 

The heat damages them over time.