Alternator Overcharges

Fig. 1 Alternator voltage output test connections:

1. Check alternator output voltage as follows:
a. Turn off all electrical loads.
b. Connect suitable charging system analyzer to system, as per analyzer manufacturers instructions.
c. Charge battery until charging rate indication becomes less than 5 amps or replace with new battery.
d. Start and operate engine at approximately 2500 RPM and note analyzer reading. If reading is less than 5 amps, proceed to 5.
e. If reading is less than 5 amps, measure voltage at L terminal at engine speed of 2500 RPM, Fig. 1. If reading is more than 15 volts at 68° F, refer to step 2. If reading is 14.4-15 volts at 68° F, alternator is satisfactory.

Fig. 2 Voltage regulator test connections:

2. Check regulator power source as follows:
a. Disconnect alternator two wire connector, then place ignition switch to On position.
b. Measure R terminal voltage at connector, then reconnect connector, Fig. 2. If reading is battery voltage, proceed to step 3. If reading is less than battery voltage, wiring harness is defective.

Fig. 3 Alternator rotor field coil test connections:

3. Check rotor coil as follows:
a. Disconnect battery ground cable, then disconnect alternator B terminal.
b. Measure resistance between alternator L and F terminals, Fig. 3. If reading is 3-6 ohms, a faulty regulator is indicated. If reading is other than 3-6 ohms, a faulty rotor coil, slip ring or brushes is indicated.