The water collector tray under the windscreen (where the wiper mechanism sits) blocks up with leaves and dust. The water cannot drain, it stands, and it runs into the cabin: typically into the front footwell, often on the passenger side.

Control units and wiring harnesses run under the footwell and in the sill, and they corrode. That is where the apparently unrelated electrical faults come from. The rear washer system is a separate water ingress point on the same model.

The tray has to be cleaned out once a year, and that takes about ten minutes.