Originally Posted by modifry

Actually, a blown fuse or bad relay would NOT take out both lights, as the low beams are separately fused. Same for the relays - one for each side.

Assuming he has a pre-DRL car, it's unlikely that one fuse or relay is bad, otherwise the bad side would be flickering.*
If he does have a DRL car, I would look first at the fuses and relays just because they are easy to check.



* Because of the way the S2000 is wired, if one fuse or relay is bad and you turn on the low beams, the HID on the bad side will flicker and both HIGH beams will come on real dim. The headlight wiring allows power to back-feed through the high beam filaments to the HID with the blown fuse or bad relay, but since the voltage is reduced by going through both high beams the HID flickers. You can test this yourself if you have a pre-DRL car. Wiring on the DRL cars is different so I don't think it will back-feed, but I never tried it when I had my '08. However, the DRL cars still have separate fuses and relays for each HID.