Another way to get your headlight door to stop in the middle position, so you can replace a headlight, is to turn on your headlights, so the doors open all the way, then push the headlight switch in (off) for just a short time, then quickly pull the switch out to the parking light position. The rotation will stop, and the headlights will be off.
If you try to rotate the knob, like you did, the circuitry will try to close the headlight again! You'll need to disconnect the battery, if you want to rotate the knob manually.
:cool