Hello Christopher
probably one (or more) of the following:
Bad relay
Poor contacts on your wiper stalk
Corroded fuse contacts
if your "high" speed wiper function is controlled by a centre console switch, bad contacts there
corroded wiring, check the "multiplug" that connects the wiper motor to the wiring harness
Doubtful, but possible, problems with the wiper motor contacts that are used for the park function
Tin of contact cleaner and a multimeter will prove helpful!
Let us know how you get on
Malc