I have a 2006 IS350 with the upgraded 2012 headlights (stripped) from Sewell and Philips 6000K Ultinon bulbs. Occasionally, the passenger-side head light bulb will refuse to turn on for short periods at a time.

Does anyone know if this would be symptomatic of a bad headlight housing, bad ballast, bad bulbs, or something else?

 

Swap the passenger side bulb to driver side and driver side bulb to passenger side. If the driver side is causing issues, its your bulb. If the passenger side is still not working, its your passenger side ballast.

 

Good idea, thanks!

 

^^Exactly what I was about to say! Same thing goes for "faulty" coilpacks; swap them around to see if the issue follows the coilpack or the cylinder.

 

My passenger headlight was out again tonight, so I swapped the light bulbs as @idoke1 suggested. Afterward, both headlights started working again. However, check this out: http://imgur.com/a/8APzK

The passenger ballast connector looks pretty messed up (even though it still works). Also, the passenger-side light bulb had some strange discoloration compared to the driver-side light bulb.

I'm leaning toward getting new passenger-side ballast — I doubt the connector comes separately. Anyone have any better ideas?

 

It looks greasy and it may have some corrosion. Clean it first. That could be the issue and not the ballast.

 

Hit that connector with some dielectric grease.