Here's the short version - The dynamo works and has passed all tests. It passes a charge to D on the cut out. The ignition light remains on, the ammeter def works and shows a 4 amp discharge when engine running, more if light on. If I connect the battery to A on the cut out I only need to touch it gently and the contacts close. If I start the engine the contacts remain closed. If I disconnect the battery and put 7 volts through the d+ contact on the cut out nothing happens. The contacts can be pushed shut but immediately open again. If I put 13 volts through it the cut out closes and opens with every contact. The ignition light only comes on if its earthed to the car, but remains on anyway.
Seems to me the cut out needs recalibrating?
Comments please?

Would be worth making sure that you have a really good earth connection to the cut out. From your description it sounds like there's a problem with the voltage coil, they usually work or they don't, but a bad earth would give the symptoms you describe.

Location: N W Kent

I had the same problem,it was cured by running a separate wire from the cut out box to earth. The cut out would not earth from casing to bulkhead as it is supposed to.