After replacing the ballast, the headlight on the driver's side keeps going off.
There are 3 items in the xenon light circuit responsible for igniting the bulb. According to Infiniti's TSB on xenon light, they recommend replacing the bulb first, and that will solve most problems.
The HID control unit, and the harness with the bulb socket, (called the starter,) are also replaceable. The HID unit and starter are usually sold together as one unit. If you have replaced this, then the bulb would be the next logical part. Swapping of parts from left to right, one-at-a-time, to see at what point the malfunction moves from the left side to the right side, is really the only way to diagnose this type of issue. You may want to enlist the help of a mechanic, such as one from YourMechanic, who is trained in the diagnosis of xenon light circuits, inspect the issue with your headlight system, and recommend the best path to repair.
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