BTW, the W/S "switch" is not a contact type switch, it moves a plastic vane in, or out of the path of a photocell pair. ( I think, at least that's how it looks to me, I have a disassembled shifter assembly )
SO, if there is something else blocking the photocell, then the switch would be ineffective.
( Leave it to the Germans to over-engineer a simple function )