Hi which model and year car are we talking of ? I imported a '28 Commander to the UK which came with an 8 volt battery which needed replacing but before I did I put the volt meter on the dynamo out put wire and it was reading 19 volts so I moved the third brush which reduced the Voltage ,I removed the primary electrical supply wire and tried a 12 volt battery obviously the motor was spun faster but not dangerously so , I then changed bulbs etc and have now been running on the 12 Volt battery for some years it has made it easier to fit such things as an LPG system .Bill