Why fit the extra alternator/dynamo? The original one is more than adequate and if it's knackered just get it rebuilt. A classic deserves to be properly maintained with original parts or the correct rebuilt parts.
Have another look. The stand-by magneto is to the rear of the dynamo, on an extension shaft fitted with a manually operated dog clutch. This is used if the coil expires, and it sends HT via the yellow wire, to the rotor arm in the distributor. The extra alternator I mentioned is the one fitted to the front of the engine and driven by a belt. This is above and to the front of the dynamo. As I said before, this is not necessary and detracts from an original car. Why do people think they need to 'improve' these old cars?
