Right, i have a problem with the rear wiper. It started a little while ago, when i put it on, it wiped just under half the screen and stopped

Every time i did it, it would park in funny places, each time doing sort of half a wipe... My first thought was relay, its not supplying the power for long enough. Replaced, same problem.
Next, i took the linkage out, cleaned it up, and greased the spindle, common problem with rust i gather... Same problem.
Next, i tried a new motor, which worked perectly in the donor car, doing the whole wipe, put in mine, same half wipe problem!
Now i dont know where to go! I've done everything i can think of!
Help! Could it be the fusebox, as i have had a few probs with the fog light, whic i believe is the fusebix?
Thanks
