Thanks for that Mark, I appreciate your time and effort. I am now considering passing this thing on to my auto-electricain colleague because I am venturing too deep into areas where I am not confident of making a positive diagnosis. I have re-read Dave Hill's excellent article on volt-drop testing which I understand, but that combined with scoping, I fear that after a few more hours on this thing I will be left with a jumble of information which I do not understand and cannot up-load on this site. Anyway, I shall sleep on it and see how it hangs tomorrow.

Kind regards

Pete

PS: Hoping they find the broken earth point which Jim alluded to!