Toyota Pick-ups/Land Cruiser/4Runner 1970-1988



See Figures 1, 2 and 3

The alternator converts the mechanical energy supplied by the drive belt into electrical energy by a process of electromagnetic induction. When the ignition switch is turned on, current flows from the battery through the charging system light (or ammeter) to the voltage regulator, and finally to the alternator. When the engine is started, the drive belt turns the rotating field (rotor) in the stationary windings (stator), inducing alternating current. This alternating current is converted into usable direct current by the diode rectifier. Most of this current is used to charge the battery and to supply power for the vehicle's electrical accessories. A small part of this current is returned to the field windings of the alternator enabling it to increase its power output. When the current in the field windings reaches a predetermined level, the voltage regulator grounds the circuit preventing any further increase. The cycle is continued so that the voltage supply remains constant.

All models use a 12 volt alternator. Amperage ratings vary according to the year and model. 1970-79 models utilize a separate, adjustable regulator, while 1980-88 models have a transistorized, non-adjustable regulator, integral with the alternator.

Click image to see an enlarged view

Fig. Fig. 1: Exploded view of a typical alternator-1970-79

Click image to see an enlarged view

Fig. Fig. 2: Exploded view of an alternator with an IC regulator-1980-88 (except 3F-E engine)

Click image to see an enlarged view

Fig. Fig. 3: Exploded view of an alternator with an IC regulator-3F-E engine


To prevent damage to the alternator and regulator, the following precautionary measures must be taken when working with the electrical system.

  1. Never reverse the battery connections. Always check the battery polarity visually. This is to be done before any connections are made to ensure that all of the connections correspond to the battery ground polarity of the truck.
  3. Booster batteries must be connected properly. Make sure the positive cable of the booster battery is connected to the positive terminal of the battery which is getting the boost.
  5. Disconnect the battery cables before using a fast charger; the charger has a tendency to force current through the diodes in the opposite direction for which they were designed.
  7. Never use a fast charger as a booster for starting the truck.
  9. Never disconnect the voltage regulator while the engine is running, unless as noted for testing purposes.
  11. Do not ground the alternator output terminal.
  13. Do not operate the alternator on an open circuit with the field energized.
  15. Do not attempt to polarize the alternator.
  17. Disconnect the battery cables and remove the alternator before using an electric arc welder on the truck.
  19. Protect the alternator from excessive moisture. If the engine is to be steam cleaned, cover or remove the alternator.


See Figures 4, 5, 6 and 7

On some models, the alternator assembly is mounted very low on the engine. On these models, it may be necessary to remove the gravel shield and work from beneath the truck in order to gain access to the alternator.

  1. Disconnect the negative battery cable.
  3. Remove the alternator pivot bolt. Push the alternator in and remove the drive belt.

Click image to see an enlarged view

Fig. Fig. 4: Belt tension adjustment

  1. Pull back the rubber boots and disconnect the wiring from the back of the alternator.
  3. Remove the alternator mounting bolt and then withdraw the alternator from its bracket.

To install:
  1. Position the alternator in its mounting bracket and lightly tighten the mounting and adjusting bolts.
  3. Connect the electrical leads at the rear of the alternator.
  5. Adjust the belt tension as detailed in Section1.

Click image to see an enlarged view

Fig. Fig. 5: Loosen the bottom alternator adjusting bolt

Click image to see an enlarged view

Fig. Fig. 6: Remove the bottom alternator adjusting bolt--note the location of the top alternator bolt

Click image to see an enlarged view

Fig. Fig. 7: Remove the alternator assembly