I have HID lamps with the standard off/on/auto/front-rear fog light switch.
I have recently developed the following problem.

With the switch in auto position intermittently the left lamp does not illuminate. It does not matter if it's wet or dry outside. It may go for days/weeks without a problem and then one night it will constantly have the issue, ie out shopping with multiple stops.
When the lamp does not illuminate I place the switch "off" then to "on". Both lamps illuminate with the left lamp dimmer than the right, but then after a few seconds both lamps are the same brightness. When I run the lights in the manual mode they both always illuminate together.

Does anyone know if I have a problem with the switch, the exciter, or the bulb itself?

 

Jeffp, from what you are describing, your problem is most likely isolated to the left headlight assembly. The auto lights and the normal lights both power the same relay to make the lights come on. So, whether you use either position should have no affect on whether the headlight will work or not.

What I would tell you to first try is switching fuses F29 and F30 in the engine bay fuse box. If your problem switches to the other side, you have a bad fuse. Next, I would pull off the plug for the left headlight and look at the pins. It is very possible that the pin is recessed slightly and it is making intermittent connection and leading to the light flickering on and off like you are seeing.

After that, you would need to mess around with a multimeter to see where you are loosing your power and go from there.

 

I'll try those suggestions this weekend.