97 Discovery rear wiper quit and delay on front wiper doesnt work same day it quit. No voltage at rear wiper checked switches and fuses all check ok. Looks like possibe mfu to check next unless any other ideas.

 

Check the ground at E201 which is behind the left footwell kick panel. Shared by both wipers/MFU. You should post in the Disco 1 section, you'll get more replies/answers.

 

Check the Rave wiring diagram and see where the two systems are interconnected. I am thinking that because the front wiper still works that it isnt a ground issue. Probably the wiper module or multi function switch.

 

I would like to add that the mfu has a relay related to it....behind the drivers side kick panel...it's the first one ...closest to the door...you can swap it with one of the others to check it....mine went and I had the exact same symptoms as you do