My 2018 300 has the Bi Xenon headlights. The left one is intermittent. Sometimes works, sometimes doesn’t. I bought a replacement bulb a couple of years ago, every time I go to replace it, the light is on. Any thoughts?

 

Replace it anyway and see what happens. At least then you will know if it's the bulb or the circuit.

 

So swapping bulbs didn’t change things, and a new ballast also didn’t change things. Swapping entire housings also left side still out. Fuse is good. Any thoughts? Am I missing something?

 

Wiggle the wires near the bulb see if it goes out when you do that or not.

 

Ok, I just did that. No luck. I also replaced the fuse, even though it showed continuity, because it had a black mark like it had been arcing. No luck. Do you think there’s also a arc on the fuse receptacle preventing a good contact? What else is in the circuit? Do you know where I can get a schematic of the headlight system?

 

It turns out that with HID bulbs there is both a left and right relay in the power distribution center. I swapped them with each other, no change. There doesn’t seem to be anything else in the circuit. I think the fuse box might need replacement if I can’t clean the terminals. Jiggling the fuses has no effect.