It didn't work. The guy who suggested it, who is, in fairness, a professional vehicle electrical technician, insisted it should and that I must have a faulty sensor or wiring. He then said that I should simply buy a complete aftermarket kit and fit that, as it will be cheaper than even one second-hand sensor. This surprised me...but he was right! A quick peruse of fleabay showed many available for a few quid. £16.00 saw a complete system delivered the next day, four sensors, control box, small colour screen and all cabling. I fitted it, with the screen unobtrusively top right of the windscreen and all cables hidden, and it works a treat, the screen giving a graphic representation of the car. A bonus is that the sensors are hard wired and potted, so should be impervious to bad weather.