Hi Jo,
The point I had tried to make was that the corrosion was not sufficient to prevent volts from arriving at the light fittings, all twelve of them were there, absolutely no doubt about it. The problem was that the green corrosion on the ends of the plain copper wire was stopping the amps, needed to light the bulbs up, from getting through. An AVO meter reading of twelve volts will not therefore provide the whole story. Effectively it can be likened to a leaky water tap that is jammed solid so that you cannot move it, but still allowing water to dribble out. It will let your water hose fill up after a week or two, but that's not much good to you if you want to fill your water tanks in the next ten minutes.