Change Polarity

By Norman Nock

Originally published in the Austin-Healey Magazine, June-July 1983


Many of you have asked me, how do I change my Healey to a negative earth or as we say away from the manual, negative ground.


First, remove battery and reverse to allow negative side of battery terminal to go to ground.

If your car is fitted with the original Lucas type battery lugs, (die cast) the negative lug inside taper is too small to fit the larger, positive terminal of the battery. Change the lugs or replace them with the clamp type.


Secondly, remove both wires from the generator using an extra piece of wire joined to the hot (opposite) side of the battery at the starter solenoid. Touch the other end of the wire to the small terminal of the generator and hold it there for two seconds. This is to polarize the field windings and cause the generator to change the battery in the opposite direction.


Thirdly, inspect the coil terminals to find their markings, negative – or S.W. This terminal should be connected to the wire that goes to the distributor. If there is a second wire on the same terminal that goes to the cut off ground switch, this will need to be changed together with the wire that goes to the distributor. The positive or + or S.W. terminal should be connected to the wires that go to the ignition switch and fuse block. The change is done to make a ‘negative spark.’ (Refer to HH April ’83) If you are not sure of how to change these wires on the coil leave them as they are, the engine will still run O.K. but you will lose about 10% of your spark efficiency.


Fourthly, if your car is equipped with an electric tach, it will no longer work due to the wrong polarity. The tach will have to be removed and sent to an instrument repair shop to be changed to work on negative ground. If you have trouble finding a shop to handle this job, may I recommend Speedo Meter Service, 131 Fell Street, San Francisco.


Lastly, if your coil is marked SW and CB at the terminals it is an original type coil made to give maximum spark on positive ground. Now that you have changed to negative ground and reversed the terminals you will still lose 10% of its maximum capabilities. The only answer now is to install a Lucas coil. Look forward to seeing you at Eureka 83 during the Lucas Tech Session. Have your pencil and paper handy.


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