Alternator Undercharges

Current Output Test
1. Connect test leads of charging system analyzer tool 078-00005 or equivalent to vehicle, following tool manufacturer's instructions.
2. Turn on all electrical accessories, then start engine and allow to run between 2500-3000 RPM.
3. Read and record maximum current output. Current output should be within 10 percent of rated alternator output.
4. If current output is within specifications outlined in previous step, alternator is functioning properly. If current output is below specification, proceed to ``Voltage Output Test.''

Fig. 1 Voltage output test connections:

Voltage Output Test
The following test must be performed with a fully charged battery.
1. With charging system analyzer connected as outlined in previous test, start engine and run at approximately 2500 RPM.
2. With all electrical accessories off, read and record current output.
3. If recorded reading is less than 5 amps, proceed to next step. If current reading is greater than 5 amps, voltage loss in charging circuit is indicated. Check battery, alternator and engine ground cable connections. Clean or repair connections as necessary.
4. 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.
5. If reading obtained at ``L'' terminal is less than 14.4 volts, proceed to ``Regulator Power Source Test.'' If reading obtained is 14.4-15 volts, a problem exists in alternator stator or rectifier.

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 battery and ``R'' terminal.

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, field coil is satisfactory. Proceed to ``L Terminal Voltage Test.'' If reading obtained is other than that specified, a problem exists in the rotor, slip rings or brushes.



``L'' Terminal Voltage Test
1. Reconnect battery ground cable and output wire to ``B'' terminal at rear of alternator.
2. With ignition switch On, connect voltmeter positive lead to ``L'' terminal metal connector, and negative lead to alternator case. Read and record reading.
3. If reading obtained in previous step is 1-3 volts, a problem exists in the stator or rectifier. If reading obtained is above 3 volts, a problem exists in the regulator.