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Brake Switch Test

  1. Ensure fuse marked "gauges" is okay (most models). Check for 12 volts at both sides of brake switch(es). Some GM vehicles have 2 electric switches at brake pedal. One switch will have 4 wires and the other switch will have 2 wires and a vacuum hose.
    NOTE: Either of these switches can be used for lock-up. To avoid misdiagnosis, check both switches. If upper switch with vacuum hose is used, check 2 wires at that switch. On 4-wire lower switch, check 2 wires farthest from plunger.
  2. Ground test light. DO NOT  depress brake pedal. Turn ignition on. Check wires for voltage. Voltage should be present at both wires. Depress brake pedal and retest. Only one wire should have voltage.
  3. If brake switch did not pass previous test, remove brake switch and repeat step 2), pushing and releasing brake switch plunger. If brake switch fails test, replace switch. If brake switch is okay, adjust switch as necessary.
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