Prior to the advent of alternators, generators were used to recharge batteries and produce current for the electrical systems in vehicles and heavy and agricultural equipment. Just as electrical systems powered by an alternator, 6-volt systems require a voltage regulator to prevent the battery and generator from burning up light bulbs, blowing fuses and melting the electrical system. Testing the generator and regulator on a 6-volt electrical system is not difficult. All tests are conducted from the battery. Many of the tests are conducted from the battery.
Make contact with the positive multimeter probe to the positive battery terminal and the negative to the negative, with the engine off. The multimeter should display more than 6 volts by a several tenths; 6.4 to 6.8 indicates a healthy battery. If the battery output is less than 6 volts, recharge the battery and test it again. If the poor output persist, replace the battery.
Ask your assistant to fire the engine. The multimeter display should increase to between 6.8 and 7.4 volts if the generator is working properly at idle speed. If there is no increase in voltage, the generator's brushes are faulty or not making contact with the inside of the generator wall. In this case, rebuild or replace the generator.
Ask your assistant to slowly rev the engine to increase the engine rpm. The multimeter should indicate a steady climb in the voltage, then stop at around 7.8 or 8 volts. If this occurs, the regulator is functioning properly. If the voltage continues to climb beyond the 8.2 voltage mark, the regulator is failing. In this case, troubleshoot the regulator.
Disconnect the battery, negative terminal first, then the positive. After several hundred hours of operation, the contact points foul. This can cause the regulator to fail to manage the current voltage. To remedy this problem, file the contact points on the regulator. First, remove the positive and negative wires from the armatures by loosening the screws on the mounting bracket located on the side of the regulator, then pull the wires free from the armatures. File away the corrosion on the armatures. Reattach the positive and negative wires to the armatures and replace the bracket and mounting screws. Test the regulator.
Test the air gap by pressing down on the armature lever, located on top of and to the side of the shunt winding, with your fingers. Make sure all the contact points on the winding touch the bottom of the lever simultaneously as you push down. If not, bend the armature -- next to the set screw -- until it closes all the contacts at the same time when you press down on it.
Adjust the point opening on the regulator by bending the upper armature stop up slightly -- no more than 1/16 of an inch. It is a tab located on the side of the middle winding's framing. It presses down on the top of the framing of the shunt winding. Bend it up by sliding a flathead screwdriver between it and the framing of the shunt winding.
Connect the battery. Positive terminal first, then the negative. Test the closing voltage -- the point at which the regulator stops the increase of voltage released into the circuit. To do so, ground the negative multimeter probe by touching the frame of the vehicle, then touch the positive probe to the generator -- marked "GEN" -- terminal. Have your assistant rev the engine and check the multimeter display. When the armature stop makes contact with the contact points, the reading on the multimeter indicates the closing voltage. To adjust closing voltage, turn the adjust screw to clockwise increase or counterclockwise to decrease the tension of the armature. The greater the tension, the more voltage required to force the armature down onto the contact points. Set the closing voltage between 7.8 volts and 8.2.