Rear wiper

I am having a problem with the rear winshield wiper on my 98 explorer. When I turn the switch on while the blade is in the rest position, the wiper doesn't move but I can hear the motor working. When I push up on the blade, the wiper starts works normally. When it is turned off, the wiper returns to the rest position, however, when I turn it back on, the process repeats itself. Any help would be appreciated.