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Re: Battery

The question of "why positive earth ?" has been asked many times over the years, and I have never seen a full and satisfactory reply. In my opinion the only thing which just might be true is determining which parts of the car and wiring are prone to corroding away due to any leakage current flowing in an electrolytic cell, i.e. the situation where two dissimilar metals are separated by an electrolyte such as damp insulation,impure water or acid fallout from the battery. I suspect that Lucas based their recommendations more on percieved theory than any extensive practical investigations.

The question of needing negative spark plug polarity is a red herring, as it is just as easy to manufacture an ignition coil for either system. Even if you are forced to use the "wrong" coil, swapping the LT connections will restore the desirable negative spark. The only downside is that the autotransformer action is then reversed, which will reduce the HT voltage by about 2%, hardly worth worrying about. When ignition systems were feeble the reduction in firing voltage for negative spark (only when the plugs were hot mind you) was helpful, these days it is of less importance.

The theory I most like is that positive earth cars emit red smoke rather than black when there is an electrical fault, which helps pinpoint the location.

Location: New Forest