1. So, we can assume you have negative earth, yes or no? This is important, please answer.
2. Polarizing your dynamo: with dynamo fitted attach a wire to the live side of your battery and flick the other end several times against the "F" terminal on the dynamo. "F" terminal being the little one. They often do feel a little loose where they come through the end plate, as long as the insulation is sound and it is connected inside to the field windings you should be ok.
3. Disconnect the "D" and "F" connections at the CVC. Connect a voltmeter between "D" lead and earth, Run the engine at approximately 1500 RPM. Voltmeter should read 1.5 to 3 volts. Now connect ammeter between the "D" and "F" leads. Run the engine increasing revs until the voltmeter reads battery volts. Ammeter should now read 2 to 3 amps. If different readings are obtained repeat these tests direct at the "D" and "F" terminals of the dynamo. If correct readings are now obtained, you have faulty wires or connections between dynamo and CVC.
Make sure that the earth connection to your CVC is clean and sound. ("E" terminal). You can attach a temporary earth lead to a good earth point to test this.
You can also remove the dynamo and connect it up to the battery. Earth to the casing and the live lead to BOTH terminals. The dynamo should "motor" and there shouldn't be excessive sparking at the brushes. (Too much sparking means worn or poorly contacting brushes). This test is NOT a sure proof that the dynamo should be charging properly but it is a good test of the brushes and commutator.