the park switch is full of verdigris. you will have to remove the whole wiper assembly, take it apart and clean the switch with contact cleaner.
you'll see this comment or similar has been made by me quite a few times recently for different things. this time of year and following the crazy cold snap we had before Christmas and subsequent thaw with high humidity but still cool temps, things like switches get corroded because the moisture drops out the air on the small but cold metal of the contacts and you end up with this sort of weird fault. normally there is enough protection from the body of the switch and the boot on the plunger but when it's cold the water vapour in the air is denser so it works it's way in to stuff it doesn't normally. to prevent it happening again, dielectric lubricant can be applied to the contacts (which it would have had originally but will have all gone now) but to be honest it isn't worth it.