THE MINI MAG. Volume 2 No.8
  August 2000

Vol.2 Home Page | Index Page

By Jim Haydon.
The following articles are sourced from personal experience, experiences of others, plus publications by B.M.C., Leyland, Rover, Scientific Publications, Australian Classic Car, U.K. Practical Classics, Sports and Classic Cars Aust., Paul Hamlyn, Gregory’s Publications and others.


Many older applications of the Lucas generating systems were positive (+) to earth. These included the electrical systems on Austin, Morris, Wolseley, MG. Riley, Jaguar. Rover, Land Rover, Hillman, Humber, Sunbeam, Standard and Triumph vehicles. There is no advantage in altering the polarity to negative (-) to earth unless a modern sound system is being installed.

1. Remove the battery. Alter the terminals so that the negative (-) cable now goes to the body or chassis of the car and the positive (+) cable goes to the main power supply point. This can be either the starter motor or a solenoid depending on the make or model of vehicle. Reinstall the battery. The negative (-) lead will now go to earth.

2. Remove the fan belt from the generator pulley. Make sure the pulley can rotate without interference.

3. Take the cover off the voltage regulator.

4. Under this cover there are 2 separate coil windings. When looking at the unit from the front (with the terminal blades or grub screws at the bottom) the left winding is the voltage regulator and the right winding is the cut out. Firmly press the lower moveable contact on the voltage cut out. Hold down for 30 seconds to a minute. The generator should now spin like an electric motor as the current flow is effectively reversed. This will alter the polarity in the generators field windings.

5. Swap over the low tension leads on the ignition coil. If a 1940’s to mid 60’s radio is fitted, it will probably have a polarity switch under the unit marked + or -. Alter this switch. If an amp meter is fitted it’s wires will need reversing.

6. Replace the fan belt. The car is now negative to earth and can be fitted with modern sound equipment. Wipers, starter, fans etc do not need altering. They will run as before.

Jim Haydon.