The voltages from dynamos which have been ‘upgraded’ with 12v coils will of course be proportionally higher.Also, my bike has been re-wired so don’t go by the colours of the wiring shown as these will almost certainly be different to your bike.The Lucas dynamo types that this article specifically applies to are models E3L, E3LM, E3N and E3NL.

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This guide to testing a Lucas dynamo is based upon my experiences with my 1951 Matchless G3LS, although the same principles should apply to other Matchless and AJS bikes (and indeed to other bikes and cars of the same era which also use the Lucas dynamo charging system).

The aim is to guide you through a series of tests that can be performed with the dynamo still installed on the bike to check that it is working correctly and giving an appropriate voltage output, or to help to pinpoint potential problems if not.

Note that the voltages described are applicable to the standard 6 volt dynamos and to those which have been reconfigured to give 12v output using a modern electronic regulator.

I suspect it is basically the same as the Lucas E3N model as it is stamped with a “5” and seems to give about 5 Amps output which is the same as quoted for the E3N.

It is also stamped with a “54” which I am assuming is the year which would mean it is a non-original replacement for my 1951 Matchless.The easiest way to test a whether a Lucas dynamo is working correctly with it still fitted to the bike is to disconnect the output wires and check what voltage it is producing.Models E3L and E3LM are both 60 Watt units; the difference between them is only the design of the mounting plate for fitment to the engine crankcase or Mag Dyno respectively.Model E3N is a shorter unit which only gives 45 Watts output, and the E3NL is just a slight variation of this.However the same principles can be applied to all types of Lucas dynamo.The dynamo fitted to my bike is a Lucas model “E3NL.0” although I haven’t found many references to this model number elsewhere.