40 Merc under-dash switches

[Clem Clement]

I'm gingerly exploring my 40Merc. Under the dash on the driver's side there are a rheostat knob for the dash lights and an no/off switch. The dash has mounting holes for the switch which seem factory. I see nothing on the wiring diagram. When I first bought the car in 1956, it had a driver's side spotlight which is now gone.
Gone is the day when I could work upside down... (I turned the switch on and beer flowed out of the horn button...that is factory , right?
Merry Christmas,
Clem