Rear wash/wipe defective

After a brief period of intermittently stopping in mid-wipe, both the rear wipe AND wash packed up at the same time. The fuses are all good (three are mentioned) but I cannot find the relay for this which is rumoured to exist - anyone know where to look? I believe there is also a pcb within the wiper motor body which may also control the whole wash/wipe sequence - can anybody enlighten me on this? As usual, BMW dealers won't divulge anything of help unless you book your car in to be investigated and worked on at their extortionate labour rates, eg: £85+ per hour !! Help would be appreciated.