If a check of the wiper motor parking switch checked out OK then use an
ohmmeter between pins 53 (Green/Black) and 53e (Brown/Green) of the wiper
motor wiring harness with the wiper switch in the OFF position. This will
check the OFF/PARK contact in the wiper switch. My Bentley seems to be
missing the connecting wire on that particular diagram(84 4000s Q)...shows up
on other 4K series though. This would check the wiper switch and the contacts
in the wiper relay.