Hi Bob, I hope you are still with me! You are right!
I have at last managed to get round to looking at the solenoid, and what seems to be the problem is the pin below the contact bar, that is held on with a split pin, has worn down or broken so that it is no longer long enough to lift the contact bar and break the contacts on the high power solenoid.
I must admit I am a bit puzzled as to how this has got worn, anyway I can make another one. I assume it’s length is such that it sits just below the insulated pad on the contact bar.
I did notice that when I ran the generator and lifted the contact bar with a screw driver the voltmeter rose from a negative discharge to zero, which was good in that it showed the contacts were breaking, however I would have expected it to show a charge as the batteries should have been charging then. I checked the fuses in the box where the battery leads come in, they were ok, any ideas?