What is this toggle switch for?

440plus6 said

I have a switch in a similar location on my 73. It is for the rear window heater (defroster).

Click to expand...

And I have the same exact thing that says "Map Light" with a black plastic bulb socket on the passenger side under the edge of the dash.
Mine was not messed with and it still works so I know that's what it was on my car originally.