Passenger HID headlight not working

I have already replaced the bulb with a new Philips bulb from Amazon and that didn't get the headlight working so I bought and installed a new ballast and that didn't work either. I did some checking and the voltage at the connector that plugs into the headlight to power the ballast has less than 12V, actually closer to 11 than 12. Checked the battery voltage in the computer and it says 12.1V. The battery is relatively new, less than two years old. I removed the headlight assembly and using jumpers connected the input terminals at the dust cover to the battery terminals on my truck and the headlight fired up. So it seems for some reason I'm not getting enough power to the left headlight to make it fire. I checked the wiring as far as I could back to the firewall and it seems fine from a visual inspection. Any ideas where to check next? The drivers side headlight works fine.