I am attempting to cleanup/redraw the electrical diagrams for the S Series but am confused by the symbols on the Supplement sheet see below - what do the little circles represent? I dont think they show earth connections, could they represent some form of sheilding??
You're bang on with the shielding - that's exactly what it is.
Being signal wires from the distributor, any electrical noise would be detrimental to the smooth running of the engine, so the wires are individually shielded and connected together at a common earth point.