316 compact wiper problems

Hi - I have just joined so please excuse my ignorance. I have a problem with the wipers on my 1997 316i Compact - when on itermittment the get stuck half-way up the windscreen AND the rear one - once on just carries on going. On Normal they do not do this at all - I have taken them to a garage who have said it is the windscreen motor which doesn't make sense surely as the others work :confused:

I have had a read and asked friends who have said it may be the relay - is this possible and has anybody had a similar problem - any advise would be greatly received.

Thanks

Sarah