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Positive or Negative Earth



Most old British cars with the exception of a few left the factory with the positive terminal of the battery connected to the frame or chassis of the vehicle.

If your vehicle is already negative earth already then that's good.

Converting to negative earth is an easy affair though.

Remember, with negative earth you can run all sorts of more modern equipment via your cigar lighter with any age of car or bike

i.e. Sat Nav - Phone Charger - Laptop computer (with an adaptor) etc

If your motorcycle is 12v or you've upgraded from 6v to 12v then with a negative earth regulator you can install a hidden cigarette lighter socket. With this you can charge your mobile phone on the road or even run a Sat Nav on your classic. Handy for powering that electric pump to inflate your airbed when camping too......


Worth thinking about before you order a regulator.

Starter motors, wiper motors, heater motors and lighting accesories aren't polarity sensitive. In fact most accessories aren't polarity sensitive with the exception of the electric clock and most radio's. Connect a positive earth clock to a negative earth and it won't work again and vice versa. So, look out for the same type of clock at jumbles or on ebay but one that is negative earth. Most older radios (up until around 1970) were positive earth

Some older radio's have a dual polarity with a simple switch to change it. Most radio's are either one or the other so check before connecting or the set will be damaged. Modern radios are usually negative earth. 


So, with any polarity sensitive items changed (if any), swap your battery leads around so that the negative post is now connected to the chassis. Any other wires that were connected the negative battery terminal should be connected in the same way to the positive terminal now.

Swap the wires round on the vehicles ammeter also.


This done, before you switch on, the only other thing you need to do concerns coil ignition. You'll see that with positive earth the positive + side of the low tension (LT) on the ignition coil goes to the distributors contact breaker points. You need to swap the coil low tension wires round so that the negative - side of the coil now goes to the points.

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