Cut out

[Tiger]

You don’t say your location I am sure if one of the seveners is near we could help!

[Dave Mann]

I gave up trying to fix a dynamo on the car, I put a link wire from F to D and connect a analogue voltmeter to D and earth and if there is no output turn the engine to No 1 cylinder firing and remove the dynamo. It is then clamped in a vice and spun with my electric drill with a voltmeter on D and the case and prodding each brush in turn, if it doesn't burst into life it's a strip down.

[k8207418]

Have you had any issues with this over time ?

[Dave Mann]

Removing the dynamo to the bench for testing permits me to see what is or isn't going on, whilst the strip down has revealed all manner of defects with the most common being broken wires between the brushes and the terminals the most common being the wire from the brush to the D terminal being worn away by he armature. Also broken field connections and one where something had got in the works and severed two armature conductors and occasionally incorrect connections between the bushes, the field and terminals. One teaser was damaged fuse holder which took a bit of care to fix. You name it I've seen it broken and trying to fix a dynamo in situ is for me a waste of time. The strip down also permits attending to any mechanical faults such as excessive end float.

[john williams]

I think you are getting too many conflicting remedies.
Start by disconnecting the "D" and "F" leads.
Connecting your voltmeter from "D" terminal on dynamo to earth. Run the engine and you should get approximately 1 1/2 volts. If not the fault is in the dynamo, usually poor "D" brush connection lead , sticking brush or faulty armature.
If you get the 1 1/2 volt on the "D" lead, bridge the "D" and "F" terminals, keep the volt meter connected to "D" terminal. Run engine you should get 7 1/2 volts. If not the fault is in the 3rd brush circuit within the dynamo. 
With the "D" and "F" leads disconnected, there should be no ignition warning light when the ignition is switched on. If the ignition light comes on with the "D" lead disconnected from the dynamo, there is a fault between the ignition switch and the "D" lead connection.
If there is no ignition light with ignition switch on and "D" lead disconnected, connect the "D" lead to earth and the ignition light should come on. This confirms ignition light circuit is good. Reconnect the "D" lead to the dynamo, switch on the ignition and the ignition light should be on. If not fault is in the "D" brush/armature circuit.