Headlight Problem
 

Passenger side headlight low beam/HID was flickering and then stopped altogether.
Replaced the bulb, replaced the ballast, still nothing. Circuit tester shows power in the gray and red wire in the plug going into the back of the headlamp housing.

High beam, fog light, side marker and turn signal all work.

Any help is greatly appreciated.

Probably the ballast. If you are god with electrical components, there are I think 4 components inside that would bee to be replaced: 2 capacitors, 1 transformer, and 1 regulator. All have either failed or are going to fail because of the failure of the other failed components.
Relatively easy to just buy a used headlight from eBay and swap out the ballast instead of figuring out the smaller components. Good luck!