Current Output Test

Fig. 2 Alternator current output test. Bosch & Nippondenso alternators:

Testing

1. Disconnect battery ground cable.
2. Disconnect "B+" lead at alternator output terminal.
3. Connect a 0-150 amp D.C. ammeter in series between alternator "B+" terminal and disconnected "B+" lead wire.
4. Connect positive lead of a suitable voltmeter to "B+" terminal of alternator, then connect negative lead to a suitable ground.
5. Connect a suitable engine tachometer, then reconnect battery ground cable.
6. Connect a variable carbon pile rheostat between battery terminals, ensuring carbon piles are in "open" or "off" position.
7. Remove air hose between Single Module Engine Controller (SMEC) and air cleaner, then ground one end of a suitable jumper wire and probe green R3 wire on dash side of black 8-way connector. Use caution not to ground J2 wire of 8-way dash connector. Both R3 and J2 wires are green on alternator side of wire connector. On dash side of connector, R3 wire is green, while J2 wire is blue.
8. Start engine and operate at idle speed, then adjust carbon pile and engine speed in increments until a speed of 1250 RPM at 15 volts is obtained. Do not allow voltmeter range to exceed 16 volts during testing.

Test Results

1. Note ammeter reading. Ammeter reading should be within specified limits noted in specification charts in individual truck chapters.
2. If reading is less than specified, alternator is defective.
3. After completion of current output test, turn off carbon pile and ignition switch, then disconnect battery ground cable.
4. Remove ammeter, voltmeter, tachometer and carbon pile, then reconnect "B+" lead to alternator output terminal.
5. Disconnect jumper wire, then connect air hose from SMEC to air cleaner.
6. Connect battery ground cable.