Before removing a generator suspected of being faulty, you should check the battery, as discussed earlier, and the generator output. Refer to the manufacturer's manual for correct generator output specifications and proper testing procedures. If the generator is operating properly and the battery, wiring, and connections are in operating condition, a defective voltage regulator is indicated in which, in most cases, the regulator is removed and replaced. However, if the generator is not producing the specified amperes at the specified engine speed, then it must be removed from the vehicle and either repaired or replaced.

Figure 2-15.- Disassembled view of a two-brush generator.

TESTING FIELD COILS.- To test the generator field, you must disconnect the grounded ends from the frame. Place one probe of the test lamp circuit on the field terminal end of the coils and the other probe on the grounded end. If the lamp lights, the field circuit is complete. However, because of the resistance in the field coil wire, it should not bum with normal brilliancy. Normal brilliancy of the test light bulb indicates a possible short circuit between the coils of the field. If the light does not burn, the field is open-circuited.

A grounded field coil is located by placing one test probe on the field terminal and the other on the

Figure 2-16.- Testing field coils for ground.

generator frame (fig. 2-16). If the test lamp lights, the field is grounded. The ground may be caused by frayed wires at the coil ends. In most cases, grounds and open field coil ends, the ohmmeter will measure the actual circuits in the field coils cannot be satisfactorily resistance of the coil. If the specified resistance of a repaired. The defective field coil must then be field coil is given in the manufacturer's manual, also replaced. obtained by measuring a new coil, you can compare values obtained through tests. For example, a short-Test for grounds, shorts, and open circuits in the circuited field coil would have practically no field coils can also be made with an ohmmeter. The resistance and the ohmmeter would register near zero; ohmmeter has test probes similar to the test lamp or the ohmmeter would register excessively high circuit. When these test probes are connected to the resistance in testing a coil having an open circuit. By following the manufacturer's instructions in using the ohmmeter, field coil tests can be made more quickly and accurately than by using a test lamp circuit.