That was my first thought when I saw the back of that plug was that it was for a 9006 bulb but it's tough to know as there are other connecctors on the car that use the same back half as that but the pins and plug center are different. Do you have a multimeter? You could always probe the pins for ground continuity and then if you find that one is always grounded regardless of the state of the ignition, then test the other side for voltage when the light switch is pulled out, when the ignition is on, when the car is started etc. If it checks out that it is on with the headlights, check to see if there is another one under the passenger side headlight or inside the fender well. Perhaps the PO removed a set of factory fogs before he sold it and left the wiring in there. I'd also check the inside driver side fender as well in case that wire was just ran underneath the bumper cover and he wrapped it around something to prevent it from falling out onto the ground when the passenger side light was removed.

Good luck