Yeah, that socket isn't used on any of the U.S. Buells. I'm pretty sure that's what the fourth wire on the Buell harness is for. You won't need it.
Also, if I remember correctly, the yellow wire goes to the white, and the white goes to the yellow in order to get the proper low/high beam. Low beam should be the bulb on the right (when you're on the bike, not facing the bulbs).