Alternator Output Wire Resistance Test

Fig. 1 Alternator output wire resistance test. Except front wheel drive:

Fig. 2 Alternator output wire resistance test. Front wheel drive:

Fig. 3 Alternator output wire resistance test:

Fig. 4 Alternator output wire resistance test:

Test Procedure

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 wire of a suitable voltmeter to disconnected "B+" lead wire, then connect negative lead to battery positive post.
5. Remove air hose between Engine Controller and air cleaner.
6. On 1988-91 models except 1991 Front Wheel Drive vans and wagons and Cherokee, Comanche and Wrangler, ground one end of a suitable jumper wire and probe green R3 wire. This may generate a fault code. Use caution not to ground J2 wire. 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.
7. On 1991-93 front wheel drive vans and wagons, connect suitable jumper wire to ground and K20 (green) terminal, at rear of alternator. This may generate a fault code. Do not connect A21 (blue) circuit to ground, as fusible link will burn.
8. On 1991-93 Cherokee, Comanche, and Wrangler, and 1992-93 full size Truck/Van, and Dakota, connect suitable jumper wire to ground and K20 (green) lead wire at rear of alternator. This will generate a fault code. Do not connect A142 lead wire to ground.
9. On 1993 Grand Cherokee, connect suitable jumper wire to ground and K20 (green) lead wire at rear of alternator. This will generate a fault code. Do not connect A61 lead wire to ground.
10. On all models, connect a suitable engine tachometer, then reconnect battery ground cable.
11. Ensure carbon pile is in OPEN or OFF position, then connect a variable carbon pile rheostat to battery terminals.
12. Start engine and operate at idle speed, then adjust carbon pile and engine speed to maintain a 20 amp circuit flow. Note voltmeter reading. Voltmeter reading should not exceed .5 volt.

Test Results

1. If a higher than specified voltage drop is indicated, clean and tighten all connectors in charging circuit. A voltage drop test may be performed at each connector to locate point of excessive resistance.
2. If charging circuit resistance test was satisfactory, disconnect battery ground cable, then the ammeter, voltmeter, carbon pile and tachometer.
3. Remove jumper wire.
4. Connect battery ground cable, then the hose between Engine Controller and air cleaner.
5. On models quipped with on board diagnostics, erase codes using DRB II test tool or equivalent.