@rkw, yes, you're correct that the 500 still has halogen headlights. Perhaps I got confused since the taillights are LEDs now.

@Ricksuiter, I didn't realize the 500 takes a non-standard 9012 bulb. That's really interesting. I imagine condensation wouldn't be much of a problem in Phoenix and I'm not so concerned about it in Seattle if I leave the system as it came from the factory. I'm more concerned about cutting the dust cap to fit an HID bulb since that'll likely leave the system open to the environment and allow moisture from the atmosphere to condense on the inside of the lens.

I'd like to hear if anybody with an HID headlight conversion has experienced this problem.