Sorry for the update delay, but wanted to try the new wiper switch before I did.
Much thanks to everyone who's replied, especially horseydug.
While waiting for the new wiper switch to arrive I've left the old switch disconnected altogether as this is the only way to stop the demonic possessed wiper motion/washer behavior.
In attempting to research the source of the trouble I've reconnected it a few times only only to discover a new problem: Now my right hand side high beam comes on as soon as I turn the ignition switch to the 'on' position. It's only the right high beam and it does this irrespective of whether the headlight switch is off or on.
With the wiper switch disconnected and the headlights turned on, pulling back on the high beam flash activates only the left high beam.
Yesterday the new wiper switch arrived ($44 from Tasca Ford). I installed it and am sorry to say that it makes no difference whatsoever.
I've also tried disconnecting the 'central timer module'and there is no change when I do.
This car has an Audiovox alarm system installed that has functioned perfectly for three years now. I've disconnected the module to test for a fault there. No change.
I have thrown in the towel and scheduled an appointment with Tasca Ford. I can only conclude that this is a shorting issue. I fear for how much it will cost to diagnose/fix this problem.
