Jeep CJ 1945-1970 Repair Information




See Figure 1

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Fig. Fig. 1: Alternator terminal identification for Motorola alternators used through 1970

All Jeep vehicles through 1964 had DC generators. In 1965, alternators were installed on the Tuxedo Park versions of the CJ-5 and CJ-6. These models were known respectively as the CJ-5A and CJ-6A. Starting in 1966, all Jeep vehicles came with alternators.

An alternator differs from a conventional DC shunt generator in that the armature is stationary, and is called the stator, while the field rotates and is called the rotor. The higher current values in the alternator's stator are conducted to the external circuit through fixed leads and connections, rather than through a rotating commutator and brushes as in a DC generator. This eliminates a major point of maintenance.

The alternator employs a 3-phase stator winding. The rotor consists of a field coil encased between 6-poled, interleaved sections producing a 12-pole magnetic field with alternating north and south poles. By rotating the rotor inside the stator, and alternating current is induced in the stator windings. This alternating current is changed to direct current by diodes and is routed out of the alternator through the output terminal. Diode rectifiers act as one way electrical valves. Half of the diodes have a negative polarity and are grounded. The other half of the diodes have a positive polarity and are connected to the output terminal.

Since the diodes have a high resistance to the flow of current in one direction, and a low resistance in the opposite direction, they are connected in a manner which allows current to flow from the alternator to the battery in the low resistance direction.

The high resistance in the other direction prevents the flow of current from the battery to the alternator. Because of this feature, there is no need for a circuit breaker between the alternator and the battery.

Residual magnetism in the rotor field poles is minimal. The starting field current must, therefore, be supplied by the battery. It is connected to the field winding through the ignition switch and the charge indicator lamp or ammeter.

As in the DC shunt generator, the alternator voltage is regulated by varying the field current. This is accomplished electronically in the transistorized voltage regulator. No current regulator is required because all alternators have self-limiting current characteristics.

An alternator is better that a conventional, DC shunt generator because it is lighter and more compact, because it is designed to supply the battery and accessory circuits through a wide range of engine speeds, and because it eliminates the necessary maintenance of replacing brushes and servicing commutators.

The transistorized voltage regulator is an electronic switching device. It senses the voltage at the auxiliary terminal of the alternator and supplies the necessary field current for maintaining the system voltage at the output terminal. The output current is determined by the battery electrical load, such as operating headlights or heater blower.

The transistorized voltage regulator is a sealed unit that has no adjustments and must be replaced as a complete unit when it ceases to operate.


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

  1. Never reverse battery connections. Always check the battery polarity visually. This is to be done before any connections are made to be sure that all of the connections correspond to the battery ground polarity of the Jeep.
  3. Booster batteries for starting must be connected properly. Make sure that the positive cable of the booster battery is connected to the positive terminal of the battery that is getting the boost. This applies to both negative and ground cables.
  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. This burns out the diodes.
  7. Never use a fast charger as a booster for starting the vehicle.
  9. Never disconnect the voltage regulator while the engine is running.
  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 an alternator.


  1. Remove all of the electrical connections from the alternator or generator. Label all of the wires so that you can install them correctly.
  3. Remove all of the attaching nuts, bolts and washers noting different sized threads or nuts and bolts that go in certain holes.
  5. Remove the alternator carefully.
  7. To install, reverse the removal procedure and adjust the belt as described later.
  9. Tighten the mounting bolts to 25-30 ft. lbs. (34-41 Nm) and the sliding adjusting bolt to 20 ft. lbs. (27 Nm).


The fan belt drives the generator/alternator and the water pump. If it is too loose, it will slip and the generator/alternator will not be able to produce the rated current. if the belt is too loose, the water pump would not be driven and the engine could overheat. Check the tension of the fan belt by pushing your thumb down on the longest span of belt midway between the pulleys. If the belt flexes more than 1 / 2 in. (13mm), it should be tightened. Loosen the bolt on the adjusting bracket and pivot bolt and move the alternator or generator away from the engine to tighten the belt. Do not apply pressure to the rear of the case aluminum housing of an alternator; it might break. Tighten the adjusting bolts when the proper tension is reached.