I'm currently having headlight but specifically lowbeam issues. I'm at my wits end with this and I really need some help.

I noticed that my left lowbeam had stopped working so like any normal human I changed the bulb, but to no avail. I have checked the igniter by swapping it onto the other headlight and the igniter is indeed working. So I don't really know what else to do. After some research I read that its most likely a "ballast" issue. I am still confused because while looking through the forms I see mentions of a "ballast" and a "headlight module" but people are using the two synonymously.
*Also both my headlights do dip up and down when the car is turned on, just no light on the left lowbeam. if thats any help*

What is the purpose of the "ballast" and what is the purpose/difference of the "headlight module"?
Also, which is which? because there are two underneath the headlight, one with a yellow sticker and one with an MB sticker.
Which would I need to replace?


Which is which?

 

Function originates @ front SAM then routes through both modules. Reluctant to have someone pull codes using Xentry (MB diagnostics) could be SAM, module(s), or headlight assembly.