I have a good customer that has an '01 TL and her headlights are both out. I ordered 2 new HID lights for her and installed them and they don't work. Checked the fusebox under the hood, both fuses for left and right headlight are good. Checked both relays and they are good too. The one thing that I noticed was that when I installed both new lights and turned the switch on, the right side one turned on but after I turned it off to diagnose the left side, it never turned back on again. Very odd. I really need some help with this one, kinda stuck. The switch does turn on the parking lights and high beams so I want to rule that out too.

 

Hey buddy. Your customer?

Anyways, switch the ballast from one side to the other. If that doesnt fix the problem, switch the ballast igniter, the wire that plugs into the ballast and hids. Also check the voltages coming from each igniter.

I just checked today since I had the same problem but it turned out to be the ballast igniter. I bought one on ebay for 70 shipped. Can be pricey. But I had the hid bulbs out of the headlight assembly and turned them since it was easier to switch parts around and I heard noise from one... Which helped me find out it is the ballast igniter. I hope that helps!