Im sure I'm not the only one that has had this happen, and quite often I might add. Where usually when the car is started, only 1 foglight will turn on, I have to cycle the foglight switch till they both turn on, (usually just 1 or 2 times).
So what I though of doing was running a wire to each of the foglights with an led at the other end, in the cabin, so that the leds will light up when the bulbs are lit up, what I don't know is, when this failure to power up happens, is it a failure at the hid ballast, or at the bulb itself? that way I know where to run the wire to in order to get a correct signal.

 

I had the same problem with one my HID's. Moved the bulbs and ballasts around to different lights and concluded that it was a bad ground. My fix was relocating the ground for the light i was having problems with. You could still have a bad bulb/ballast though.