Thanks Rasputin. I have put effort into providing good earths. Note, didn't say I've succeeded. But have put earth wires in all over the place - tail light, rear indicators, alt/reg/rec, all leading back to ring terminals at the cylinder head to head-steady bolts. Added one from the lower yoke to same as well.
Ozboy, thank you for the suggestion. Had a look and there are similar multi-function testers available. Looks like a very useful tool with the function to push power into a circuit and some of them claim to be able to check, not just continuity but the quality of the wiring even through the insulation. Might well buy one.
But my main problem is that wiring systems live at or beyond the outer limit of my understanding. Today, was trying to investigate why the starter ain't working and wondering whether I've wired the safety relay wrongly. Here's what I'm aiming at if I haven't made too many mistakes:
View attachment 150420
Safety relay is supposed to disable the starter if there's a voltage on the yellow wire from the alternator. But I can't quite see whether there's something missing - does it need a power feed?
Have managed to establish there's a good 12v reaching the coil when the ignition is ON so I suspect the bike would perhaps start with the kick. Once I put the fuel tank back on of course. With the engine running, would be able to check the bike is charging but not a lot I can do with static tests.
Tomorrow will try and investigate what is going on with the Start button - it's just weird having a switch with only one wire going into it. As said above, lack of understanding.