4. Ignition ON and cb points closed I have 0V across cb points and 6V on coil supply and 0V on cb wire.
5. Ignition ON and cb points OPEN I have 6V across cb points and 6V on coil supply and 6V on cb wire (hence 0V across coil).
Any bright ideas, Chris.
With the points open you won't see much voltage across the coil as the primary winding resistance is quite low.
I would be interested to see what the current draw is when the points are closed - can you put an Ammeter in the circuit and see?
To test the coil:
Remove the CB lead from the coil and replace it with a loose piece of cable with a bare end.
Remove the coil's HT lead from the distributor cap and hold it near something that is grounded and not painted.
With the ignition ON - do you get a spark from the HT lead when the loose wire is flicked against the frame/grounded metal ?
That will show whether the coil is working or not.
If the coil is working in isolation, but not when the ignition system is assembled, it indicates an open circuit somewhere. Check for earth continuity at the points when they are closed.
You have probably done all of this, if so apologies, but the system is quite straightforward and it should just be a matter of checking each item in sequence along its length.
My avatar shows the late Len Rich in 1970 with the bike I now have - a 1958 Ariel VH