I had a similar problem with my 93 200tdi, it turned out to be the wiring loom running through the chassis that had chafed and shorted together.
Andy
Was reading back through the thread - Waz's issue could be a contender
If you remove the LH dash trim (assuming same as mine, remove the land rover plastic oval to revel a screw) and the lower dash (I think just 3 or 4 screws) you can see where the wiring runs behind the dash
Also from the engine bay to the left of the heater box there's a plastic blanking plate - held on with 4 screws - which I presume is where the speedo drive would come through in a LH drive model. When removed you can also see the cables to the wiper motor
Think essentially there is a channel on the back of the bulkhead below where the air vents are that the cables run along, emerging behind the instrument dash.
I've not found them (but haven't looked either!), but wonder whether the wiring to the LH lights/indicator also run along there?
Reason for thinking of this is:
1) Might be of help to your work chum tomorrow night
2) If you were to run new cables from the wiper stalk to the wiper motor (and know you'd prefer not to), shouldn't be impossible to thread new wires avoiding removing the whole dash.
Conscious we've focussed on earth faults, but thinking turning more to a +ve feed issue due to touching wires. Running new would at least remove/isolate any touching wires!
Wonder whether feasible to hard wire from the stalk to the motor just passing the cables along the parcel shelf to the motor for now as a test?
Can you tell this one still has me intrigued
