Fuse 5 (windscreen wipers/washers etc.) has, with immaculate timing,started blowing constantly.  Disconnecting the wipers and the screenwashers and removing the relay makes no difference, it blows  immediately the ignition is switched on.  I'm assuming that this suggests a dead short somewhere. 

I wondered if it was water related as it was a little damp here earlier today, so sprayed WD40 and dried out the visible  wiring,  but no joy.   Any known problems to look for or is it just a question of tracing he wiring back to find the short.