Well it is not a standard fitting, sounds like someone in the past has added a switch to control some extra electrical item. Maybe front fog or spotlights? Electric aerial?
Any wires connected to the switch? If so can you see where they go?
Tony
<font size="1">1981 2L FHC Cavalry Blue
1980 3.5L V8 DHC Jaguar Regency Red - sadly sold!
TR8 FHC EFI Factory development car Inca Yellow</font id="size1">