I am a bit confused now.
For example, if my dynamo, battery and voltage regulator is set up for positive earth and I fitted a 6v to 12v step up inverter would I be able to use a 12v negative earth LED headlight bulb or (not that I am going to) fit a 12v negative earth radio?
My concern being that if a GPS speedo needs to be negatively earthed, then I might break it. I can always polarise the dynamo to negative earth to make things easy and fit a negative earth regulator.
To be honest, I was hoping that someone would come back and say a cheap £20.00 replica with a 2:1 ratio will be about OK. I just don't know the correct ratio for an A10.