In my defender, the wiper motor is quite loud. Is this normal to hear it over the 200tdi? On another note it never goes back to park, you have to time it right. I replaced both the stalk 1st and then the park switch. I was wondering if I got a faulty new switch.
Have you replaced or taken apart your wiper motors themselves? I had some originals in an 84 110 that would spin past the stop if the windshield was wet and just keep going until it was dry and there was friction keeping the arms from moving the motors past that point. I kind of liked it. Almost like automatic wipers.
What is probably happening is the arms are moving too far causing the motor to go past the park position and keep going in a circle.
if you are able to stop it anywhere in its sweep with the switch. something isn't right as its supposed to return to the park position regardless. The park position is adjustable.
As far as noise goes, clearly something land rover was not concerned with but have you lubricated yours @ all ? Its driven by a cable with a worm gear outer winding and whatever the brits were using in the 80's tends to get hard and offer sigificant resistance
to already worn wiper motors.