GM Chevy Mid-Size Cars 1964-1988 Repair Guide



See Figures 1, 2 and 3

The voltage regulator combines with the battery and alternator to comprise the charging system. Just as the name implies, the voltage regulator controls (regulates) the alternator voltage output to a safe level. A properly working regulator prevents excessive voltage from burning out wiring, bulbs, or contact points, and prevents overcharging of the battery. Mechanical adjustments (air gap, point opening) must be followed by electrical adjustments and not vice versa.

Since 1973 all GM cars have been equipped with alternators which have built-in solid state voltage regulators. The regulator is in the end frame (inside) of the alternator and requires no adjustment. The following adjustment apply to pre-1973 units.

Although standard since 1973, this integral alternator/regulator has been available as an option since 1969.

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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

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Fig. Fig. 3: Testing the regulator voltage setting

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Fig. Fig. 4: Basic charging system diagnosis


  1. Disconnect the negative battery cable.
  3. Disconnect the wiring harness from the regulator.
  5. Remove the mounting screws and remove the regulator.

To install:
  1. Make sure that the regulator base gasket is in place before installation.
  3. Clean the attaching area for proper grounding.
  5. Install the regulator. Do not overtighten the mounting screws, as this will cancel the cushioning effect of the rubber grommets.
  7. Engage the wiring harness to the regulator
  9. Connect the negative battery cable.


The standard voltage regulator is the conventional double contact type; however, an optional transistorized regulator was available from 1964-68. Voltage adjustment procedures are the same for both except for the adjustment points. The double contact adjustment screw is under the regulator cover (also on the 1964 transistorized regulator); the 1965-68 transistorized regulator is adjusted externally after removing an Allen screw from the adjustment hole.

Field Relay Adjustments (Mechanical)

As explained earlier, mechanical adjustments must be made first and then followed by electrical adjustments.

Point Opening

Using a feeler gauge, check the point opening. To change the opening, carefully bend the armature stop. The point opening for all regulators should be 0.014 in.

Air Gap

Check the air gap under the armature on which the points are mounted. Check the gap with the points just touching. The gap should be 0.067 in. If the point opening setting is correct, then the relay will operate OK even if the air gap is off. To adjust air gap, bend the flat contact spring. Some units are equipped with an air gap star wheel adjusting nut.

Voltage Adjustment (Electrical)
  1. Connect a 1 / 4 ohms, 25 watt fixed resistor (a knife blade switch using a 1 / 4 ohm resistor) into the charging circuit (as shown in the regulator voltage setting illustration) at the battery positive terminal. One end of the resistor connects to the battery positive terminal while the other connects to the voltmeter.
  3. Operate the engine at 1,500 rpm or more for at least 15 minutes. Disconnect and reconnect the regulator connector and read the voltage on the voltmeter. If the regulator is functioning properly, the reading should be 13.5-15.2V. If the reading is not within this range, keep the engine running at 1,500 rpm and perform the following:
    1. Disengage the terminal connector (four terminal connector) and remove the regulator cover. Re-engage the connector and adjust the voltage to 14.2-14.6V by turning the adjusting screw at the base of the regulator behind the armatures.


When removing the regulator cover ALWAYS disengage the connector first to prevent regulator damage by short circuits.

    1. Disengage the connector, install the cover, and then re-engage the connector.
    3. Increase the regulator temperature by running the engine at 1,500 rpm for 10 more minutes.
    5. Disengage and re-engage the connector, then read the voltmeter. A reading of 13.5-15.2V indicates a good regulator.