Alternator Overcharges

Fig. 1 Voltage output test connections:

Voltage Output Test
The following test must be performed with a fully charged battery.
1. Connect test leads of charging system analyzer tool 078-00005 or equivalent to vehicle, following tool manufacturer's instructions, then start engine and run at approximately 2500 RPM.
2. With all electrical accessories off, read and record current output.
3. If reading is less than 5 amps, connect positive lead of voltmeter to ``L'' terminal of alternator connector and negative lead to alternator case, Fig. 1. Ensure that ``L'' terminal connector remains connected during test.
4. Restart engine, run at 2500 RPM, and read and record voltage output. If reading is 14.4-15 volts, alternator is operating properly. If reading is greater than 15 volts, proceed to ``Regulator Power Source Test.''

Fig. 2 Regulator power source test connections:

Regulator Power Source Test
1. Turn ignition switch On, but do not start engine.
2. Disconnect ``R'' terminal connector from rear of alternator, then connect voltmeter positive lead to ``R'' terminal connector harness and negative lead to alternator case, Fig. 2. Read and record voltage.
3. If reading obtained is at base voltage recorded earlier, proceed to ``Rotor Field Coil Test.'' If reading is less than base voltage, check for defective circuit between ignition switch and ``R'' terminal.
4. Reconnect terminal connector.

Fig. 3 Rotor field coil test connections:

Rotor Field Coil Test
1. Disconnect ground cable at battery and ``B'' terminal wire at alternator.
2. Connect ohmmeter to ``L'' and ``F'' terminals of alternator as shown in Fig. 3. The ``F'' terminal is mounted internally and can be accessed through hole in rear of alternator. Ensure that ohmmeter lead does not contact alternator housing during test. Read and record reading.
3. If reading obtained in previous step is 3-6 ohms, a problem exists in the regulator. If reading obtained is other than that specified, a problem exists in the rotor, slip rings or brushes.