I have had a headlight out for some time and I tried to diagnose the problem today hoping that it would be an easy fix... well after swapping all components 1 at a time (bulb, ballast, and connector from ballast to bulb), and checking voltages and continuity at the car side harness and in the headlight itself, I am at a loss as to what the problem is. When I swapped the components to the other side everything worked, the problem remains in the driver side headlight but I can't figure out what it is or what else to test to see where the failure is. I will say that my high beam, fog light, and signal light work, it is only my HID low beam that is not working...

Any suggestions on what it could be? Anything else I should try to test/check? I don't mind buying a new part, I just want to figure out which one it is...