A bit late on here, as I just regiseret, but if this is still a problem I can come with some more information. This might also be good for future readers of this post
On my T4 2001 model, I start the interval of the wiper by pushing in the button on the end of the wiper-handle.
However a problem I've had is that the rear window wiper "mechanism" has gotten "to firm", so that the wiper motor fails to operate the wiper back and forth. If you listen carefully you still should be able to hear the relay(?) click with an interval.
I fixed this once, by removing the inner cover of the tailgate, and then removed the wiper motor and mechanism. (First time I did this, I broke the plastic washer thing in the center, so if you decide to do this be careful, or have a professional do it for you ...)
Mine is now stuck
again, so I need to do this once more ...
Guess regular use would have helped me keeping it moving.