Rear Wiper on 89 RR

Hi all

I am wondering if any of you could point me in the right direction with a problem that is annoying me. My rear wiper works sometimes and others it doesn't. Sometimes it works real slow and others it is normal speed. Most times it doesnt park at all. Sometimes it cuts out when it it working and wont restart without maual help

Motor or relay??? Is there a relay somwhere that covers the timing or parking and if so where would it be?

Thanks

Hugh