If your generator has been removed from your car for service work or during a lengthy restoration, you may find that once it has been reinstalled in your car, it may not generate electricity. Automotive generators need a certain amount of "stored" magnetism in the internal field windings to be able to start the flow of electricity in the windings the next time the generator starts spinning.
If the generator has been worked on, or removed from service for a long period of time, it can sometimes lose this magnetic field. Once the magnatism has decreased enough or lost entirely, the current direction will not be established, and it will not be able to produce a current flow. In these cases, the generator will need to be polarized. When the generator is being used on a regular basis this magnatism remains stored in the field of the internal windings after the generator stops spinning (engine shut off), and when the generator starts spinning again (engine started), this small amount of magnatism is enough to start the flow of electricity again. Polarizing restores this magnetism and establishes the proper magnetic direction. Before you decide this might be the problem, make sure your electrical system is in perfect order (generator, switches, terminals, wiring, regulator, etc...).
To polarize the Lucas generator, a short jumper connected to the Armature "A" and battery "B" terminals for a very short period of time (one or two seconds) will restore the magnetic field in the generator field windings.
Below are several web sites that help explain this procedure. As always, be sure to fully educate yourself prior to any service work, and keep safety a top priority.