I'm not near my Rover and I'm working from a cell phone, so I can't do any research very easily, but my first instinct would be to look for the wiper switch theory of operation on the Internet, and especially on TeriAnn's website. If she doesn't show the switch configuration there, you should be able to at least decipher what wire performs the different functions in the circuit. Google "terra nova wake an Land Rover" for the website.
What MAY be of help to you is knowledge of the way the wiper motor takes power; IIRC, There should be one wire that always hot--the wiper park wire. The other wires should only be powered when the wiper is turned on. There should be a wire going to the washer motor as well. Wire color codes can be found on TeriAnn's site and in the factory Workshop Manual.
--Mark
1973 SIII 109 RHD 2.5NA Diesel
0-54mph in just under 11.5 minutes
(9.7 minutes now that she's a 3-door).