Thanks for your reply. I am running 12volt system. I'm in the UK & the Vintage Sports Car Club here do not allow modifications such as fitting an alternator. So even for night rallies in winter you would be disqualified for running with one!! I read somewhere that the old dynamo could be "chipped" to give an output hat varied with the demand - going higher than the standard 10 amps if required but cannot find any detail on how to do it.