Interior light door switch

where is it located

The exact location is dependent upon the vehicle, but it should be close to one of the door hinges. If you would care to disclose the make, model, and model year of your mystery vehicle, someone might be able to be more specific than I can.

Many are now concealed within the latch mechanism inside the door.

sorry 1999 Mercury Sable

The switch is part of the door handle.