Thanks for all the advice - I decided to snoop around myself a bit. Started with oldford's advice - looked in book and sure enough there is a fuse - it's 10A one in the engine compartment (F18 I think) - checked it - blown. Figured this was because of the short to earth Ford reported - replaced anyway having left battery disconnected overnight. Been running the car all day - left parked for 4 hours etc - still no light so I think it's cured. Went back to first garage and they held their hands up about not knowing there was a fuse but were sure the sensors were faulty (they were very bendy when I saw them) and thought they ccaused the fuse to blow - they were happy it was fixed. Not sure what to do with the Ford main dealer - surely they should know about the fuse....