The end cap is what the bulb plugs in to and there is a regular plug that connects to the end cap. You need the end cap for sure as it seals the back of the light up.

diagram from realoem

Quote Originally Posted by 530iTouring
My body shop guy pointed out the disparity in the pins on the bulbs and the plugs on the harness. Basically it's the same plug that's on the fog lights. So, do I have him just splice in fog light plugs that mate onto the headlight bulb?

Sorry no pics of the headlight buckets side by side, but the jist is that US plugs have pos/neg paddles/plugs and the Euro has a single paddle/plug and I'm guessing the ground is in the round base of the bulb.