GM Firebird 1967-1981 Repair Guide



See Figures 1 and 2

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Fig. Fig. 1: Schematic of a common charging system utilizing a non-integral voltage regulator

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Fig. Fig. 2: Schematic of a typical charging system which utilizes an integral voltage regulator

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 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 1971 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 adjustments apply only to 1967-70 units.


  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.


Field Relay Adjustments (Mechanical Adjustment)

See Figure 3

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Fig. Fig. 3: Adjustment points for a non-integral voltage regulator

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


Using a feeler gauge, check the point opening. To change the opening, carefully bend the armature stop. The point opening for all Firebird 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 incorrect. To adjust air gap, bend the flat contact spring.

Voltage Adjustment (Electrical Adjustment) See Figure 4

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Fig. Fig. 4: Schematic for testing the non-integral regulator voltage setting

  1. Connect a 1 / 4 ohm 25 watt fixed resistor (a knife blade switch using a 1 / 4 ohm resistor) into the charging circuit 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. Disengage, then reattach 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. Detach the terminal connector (with 4 wires) 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 disengage the connector first to prevent regulator damage by short circuits.

  1. Disengage the connector, install the cover, and reattach 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.

See Figures 5 and 6

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Fig. Fig. 5: Alternator and Regulator Specifications

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Fig. Fig. 6: Alternator and Regulator Specifications (cont.)