HID Headlight Acting Up

[RoyDaGeneral]

Lately, I've noticed the left HID headlight comes on and off without any rhyme or reason. The other day, I was parking in front of a store front where I could see the truck's lights reflected thru the front glass doors of that store. I noticed the left light was out, so I turned off the light switch and immediately turned it back on, which resulted in that "dead" headlight coming back to life right away.

What could be the problem, thanks!

[born2lse]

Swap the driver and passenger side bulbs and see if the issue follows the bulb. If not then it's probably the ballast.