Headlight on/off knob fell off, WTF??

You should try the clapper mod. It is mad tyte. Not compatible with stck shift though, can't clap while shifting is a real safety issue and no one wants to mess with safety. Clap ON Clap OFF!

Seriously though it is held on with a spring clip inside the knob. Sounds like yours is clipped out.

You can probably get a new one from the Ford dealer for cheap.

Also, if your gauge window is dirty or scratched and you want to replace it now is a good time because the hardest part is getting the stupid knob off. It is usually hard to remove, not falling off like yours. I got a new guage window from Ford for $24 because mine was scratched around the trip reset button.

zTime to some billet.

This happened to me all the time when I would take the trim piece off to fix my white faced gauges because they come unglued. As stated above it is held by alittle metal clip inside. This happens due to the metal pin pushing the clip more towards to closed end of the knob. All you need to do is take a really small flathead screwdriver and push the clip more outward towards the opening at the end of the knob.