Z4 Coupe (E86) Z4 Headlight Issues

Hey Folks - new member and 1st post - hope you can help me out with the following problem:
The headlights on my 07 Z4 Coupe malfunction rather randomly, where one lamp goes out while the angel eyes stay on.

When this happens I pull over, and cycle the light switch and highbeams manually a number of times. With no rhyme or reason, one headlamp will quit, the other might turn off, or they both quit leaving only the angel eyes. Like flipping two coins trying to come-up both heads, they both eventually come back on, and I drive onwards.

Happens on long drives more frequently than short ones. I dont' think bumps in the road or moisture are factors here. Took it to the dealer and they couldn't replicate the issue... basically giving me the bird. Thinking it's a controller issue... anyone ideas on how to diagnose or where to look under the hood?

Many thanks in advance.

Could be the hid ballast or the bulb. More than likely it's a bad igniter in the bulb. I'd just order a new hid kit from ddm tuning. It's always nice to have back up parts when it comes to hid's. I've went through 3 ballasts so far.

Thanks for the input DropTop... the lights work fine most of the time, so I don't think it's the ballast or bulbs. I think I found an answer on an external site as follows:

"If the inoperative headlight varies from left to right, when you have the fault warning, we would suggest that the lighting control module may be at fault. The module is a part of the light switch, on the Z4 chassis. Therefore you must replace the complete assembly if either the switch or the module are faulty. The fault could also be in the individual light control units (I would not initially suspect the ignition elements, as the lights seem to fire-up just fine). However, it would not be as likely that both units are faulty and intermittent in the same way."