My aftermarket HID kit is wired through relays, starts up just fine, but suddenly shuts off the drivers side headlight. It clearly won't pass the cold test, but oddly after 30 minutes of commuting I turned them off and back on, and both worked fine for another 30 minutes. Any help is appreciated! PS it's an 06 R53, came with factory halogen.

 

Faulty ballast breaking down as it warms up? Try swapping them side to side to see if the fault follows the ballast.

 

It actually turned out to be the computer's pulse width modulation causing it. A 2200 millifarad capacitor solved the issue. Didn't hurt that I contacted the seller and now I have two spare ballasts though! Lol