What's the purpose of reverse polarity in electricity?

b/c for every action there is a reaction, equal to it in magnitude, and opposite of it in direction

It would be very hard to argue that one way would be better than the other. It is just common standard that we tie the negative voltage potential to ground (chassis of the car). It doesn't make a difference, except you want to have compatible equipment - for example an American car stereo could internally tie its mounting to negative, and that would make it unusable in the German car.


Hawaiian... no thats not what he is talking about..

I have never been sufficiently interested in the problem to investigate it but I did read that cars that have a positive frame (ground - earth - common) are seriously at risk of electrolytic corrosion.  This might be the case but I do not immediately see how it would be.  In any case, if a positive frame did corrode, the Germans would hardly be using it.

A more interesting question about German cars, is the question of whatever induced VW to install 6 Volts systems in the early beetles.  The headlights were so dull that you needed to light a candle to see if the lights were "on".