I had this problem where my windscreen wiper just would not stop unless I took the relay out. I took it to an official dealer and they were quoting me big figures to trace the fault and they said even then they may not find it. I did it myself and it did take a long time. It was a hidden crossover of wires caused when a crook broke in and stole the radio. My question is could somone recommend a book on car electrics as I was rather working in the dark (ha ha)