GM Cadillac 1967-1989 Repair Guide



See Figures 1 and 2

The alternating current generator (alternator) supplies a continuous output of electrical energy at all engine speeds. The alternator generates electrical energy and recharges the battery by supplying it with electrical current. This unit consists of four main assemblies, and a stator assembly. The rotor assembly is supported in the drive end frame by a ball bearing and at the other end by a roller bearing. These bearings are lubricated during assembly and require no maintenance. There are six diodes in the end frame assembly. These diodes are electrical check valves that also change the alternating current developed within the stator windings to a direct (DC) current at the output (BAT) terminal. Three of these diodes are negative and are mounted flush with the end frame while the other three are positive and are mounted into a strip called a heat sink. The positive diodes are easily identified as the ones within small cavities or depressions.

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Fig. Fig. 1: Non-integral voltage regulator charging system schematic

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Fig. Fig. 2: Integral voltage regulator charging system schematic


To prevent serious damage to the alternator and the rest of the charging system, the following precautions must be observed:

  1. When installing a battery, make sure that the positive cable is connected to the positive terminal and the negative to the negative.
  3. When jump-starting the car with another battery, make sure that like terminals are connected. This also applies when using a battery charger.
  5. Never operate the alternator with the battery disconnected or otherwise on an uncontrolled open circuit. Double check to see that all connections are tight.
  7. Do not short across or ground any alternator or regulator terminals.
  9. Do not try to polarize the alternator.
  11. Do not apply full battery voltage to the field (brown) connector.
  13. Always disconnect the battery ground cable before disconnecting the alternator lead.


See Figure 3

  1. Disconnect the battery ground cable to prevent diode damage.
  3. Tag and disconnect the alternator wiring.
  5. Remove the alternator brace bolt. If the car is equipped with power steering loosen the pump brace and mount nuts. Detach the drive belt(s).
  7. Support the alternator and remove the mount bolt(s). Remove the unit from the vehicle.

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Fig. Fig. 3: Common alternator mounting - 1977 shown others similar


See Figure 4

On Heavy Duty Alternator ONLY (100/145 amp with external voltage adjuster): after connecting the negative cable, momentarily connect a jumper wire between "Bat" and "R" alternator terminals to polarize the charging system. Start the engine and run it at fast idle for ten seconds; the charge light should go out.

To install, reverse the above removal procedure. Alternator belt tension is quite critical. A belt that is too tight may cause alternator bearing failure; one that is too loose will cause a gradual battery discharge. For details on correct belt adjustment, see Drive Belts in Routine Maintenance .

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Fig. Fig. 4: Common view of the alternator belt