I have a 99 megane coupe and last week in the bad snow, I used the rear wiper, as you would. However, it will not switch off no matter what you do. I have even resorted to pulling out the fuse that alledgedly controls this errant device to no avail.
If I can't get it fixed I am just going to have to remove the rear trip and disconnect the wiper and live without it

Guns, December 2009