Well after a few days away and a lot of thinking time, I had another go at the wiring and managed to sort out the problem. Partly came about because the original wiring on the other side of the layout was done differently and I had forgotten that I had made that change! Still to prove that it works, I took a couple of dodgy videos on my phone - apologies for the quality!
https://youtu.be/GezTazvHtYY
https://youtu.be/tfGpyX5QlOg
Still a lot of wiring to do, but I do at least feel like I am making some progress again.
MIke