Rear wiper problem

I have a 99 blazer and the rear wiper has stopped working. It still moves from the stored position to the ready position when I flip the switch. It use to work for a while and stop in the middle of the window. I can cycle the wiper by hand only when it is switched on.

How do you tell if you need a new motor or the relay/delay control(?) before the moter needs replaced?

Thanks

my 99 blazer did the same thing had to put a new moter in check out auto zone think its like $79.99