Subaru ff-1/1300/1400/1600/1800/Brat 1970-1984 Repair Guide



When the ignition switch is turned ON current from the battery passes through the ignition switch to the voltage regulator. The current then passes through a series of resistors, points and coils and sends a small amount of current to the alternator post which is connected to the brushes. The brushes contact slip rings on the rotor and pass a small amount of current into the windings of the rotor. The current passing through the rotor coils creates a magnetic field within the alternator.

When the engine is started the rotor is turned by the fan belt. As the rotor turns a magnetic current is induced in the stationary windings, or stator, located in the alternator housing.

The current induced is alternating current (AC) and must be changed to direct current (DC): diodes are used for this purpose. The technical explanation of how a diode works is not important. The diode is a form of electrical check valve, allowing the current to flow one way but not the other. A negative diode will pass current in a negative direction, and a positive in a positive direction. The positive diodes make up the positive rectifier and the negative diodes make up the negative rectifier.

The stationary windings, or stator, are wound into three sets of windings or phases. Each phase winding is connected to a positive and a negative diode. When the phase winding is passing positive current, the current will flow through the positive diode to the output terminal of the alternator. When the phase winding is passing negative current, the negative diode allows the returning current from the grounded circuit, to pass into the windings to complete the circuit.

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Fig. Fig. 1 Exploded view of the alternator

The direct current flowing from the alternator output terminal to the battery is used to provide current for the electrical system and to recharge the battery. As electrical demand increases the voltage regulator senses the need and directs more current to pass through the rotor, increasing the magnetic field. This produces greater induction voltage which increases the output of the alternator. When the requirements of the electrical system decrease the voltage regulator reduces the current flowing through the rotor, lowering the magnetic field and decreasing the output of the alternator.


Pay particular attention to the polarity connections of the battery when connecting the battery cables. Make sure that you connect the correct cable to the corresponding terminal.
If a jumper battery is used to start the vehicle, refer to the correct method of jump starting in .
When testing or adjusting the alternator, install a condenser between the alternator output terminal and the ground. This is to prevent the diode from becoming damaged by a spark which occurs due to testing equipment with a defective connection.
Do not operate the alternator with the output terminals disconnected. The diode would be damaged by the high voltage generated.
When recharging the battery by a quick charger or any other charging apparatus, disconnect the alternator output terminal before hooking up the charging leads.
When installing a battery, always connect the positive terminal first.
Never disconnect the battery while the engine is running.
Never electric weld around the car without disconnecting the alternator.
Never apply any voltage in excess of the battery voltage during testing.
Never jump a battery for starting purposes with more than the battery voltage.


If you suspect a defect in your charging system, first perform these general checks before going on to more specific tests.

  1. Check the condition of the alternator belt and tighten if necessary.
  3. Clean the battery cable connections at the battery. Make sure the connections between the battery wires and the battery clamps are good. Reconnect the negative terminal only and proceed to the next step.
  5. With the key OFF , insert a test light between the positive terminal on the battery terminal clamp. If the test light comes on, there is a short in the electrical system of the vehicle. The short must be repaired before proceeding. If the light does not come on, then proceed to the next step.

If the vehicle is equipped with an electric clock, the clock must be disconnected.

  1. Check the charging system wiring for any obvious breaks or shorts.
  3. Check the battery to make sure it is fully charged and in good condition.


  1. Disconnect the negative battery cable. Failure to do this could result in damage to the electrical system.

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Fig. Fig. 2 Tag and disconnect the alternator connections

  1. Disconnect the plug connecting the alternator to the wiring harness. Disconnect the lead wire. Tag wires for identification.
  3. Remove the alternator adjusting bolt, move the alternator toward the engine and remove the drive belt.

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Fig. Fig. 3 Loosen and remove the alternator mounting bolts ...

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Fig. Fig. 4 ... then remove the alternator from the vehicle

  1. Remove the remaining mounting nuts and bolts while carefully supporting the alternator. Remove the alternator from the engine compartment.

Now is a good time to inspect the drive belt for wear, replace if necessary.

To install:

  1. Position the alternator into the mounting brackets and hand-tighten the mounting bolts. 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 as well as belt wear. For details on correct belt adjustment, see Belts in .
  3. Install the alternator adjusting bolt and move the alternator away from the engine checking belt tension as you go.
  5. When proper tension is achieved tighten all alternator retaining bolts.