Chevrolet Full-size Cars 1968-1978 Repair Guide



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Fig. Fig. 1 no caption

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Fig. Fig. 2 Charging system schematic for vehicles with integral voltage regulators

The voltage regulator combines with the battery and alternator to comprise the charging system. Just as the name implies, the voltage regulator regulates the alternator voltage output to a safe amount. 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 vehicles are 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 adjustments apply to 1968-73 vehicles.

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


  1. Disconnect the negative battery cable.
  3. Disconnect the wiring harness from the regulator.
  5. Remove the mounting screws and remove the regulator.
  7. Make sure that the regulator base gasket is in place before installation.
  9. Clean the attaching area for proper grounding.
  11. Install the regulator. Do not overtighten the mounting screws, as this will cancel the cushioning effect of the rubber grommets.


1968-72 Vehicles

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Fig. Fig. 3 Various adjustment and checking points on external regulators

The standard voltage regulator is the conventional double contact type; however, an optional transistorized regulator was available from 1968. Voltage adjustment procedures are the same for both except for the adjustment points. The double contact adjustment screw is under the regulator cover; the 1968 transistorized regulator is adjusted externally after removing an Allen screw from the adjustment hole.


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


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


Check the air 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.


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Fig. Fig. 4 Schematic for testing the external regulator voltage setting

  1. Connect a 1 / 4 omega , 25 watt fixed resistor (a knife blade switch using a 1 / 4 omega resistor) into the charging circuit (as illustrated) 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 do the following:
    1. Disconnect the terminal connector (four terminal connector) and remove the regulator cover. Reconnect the connector and adjust the voltage to 14.2-14.6V by turning the adjusting screw.

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

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