I remember reading summut about this somewhere and I think the fault was with the reversing switch. When your wipers are on and you put it in reverse it automatically puts your rear wiper on. I remember them saying the did summut to that part and it worked. Might also be the reason your rear screen wont go down, if it thinks the wiper is on.My rear wiper wont turn off when its on and I have tried a new wiper motor and switch's.