Test # 3 - Checking For 12 Volts Across Brake Switch
TEST # 3CHECK FOR 12 VOLTS AT BOTH SIDES OF THE BRAKE SWITCH
^ Check for 12 volts at both sides of the brake switch. Some GM vehicles have two electric switches at the brake pedal. One switch will have four wires and the other switch will have two wires and a vacuum hose.
IMPORTANT
Either of these switches can be used for lock-up. To avoid mis-diagnosis, check them both. If the upper switch with the vacuum hose is used, check the two wires at that switch. On the four wire lower switch, check the two wires farthest from the plunger.
^ Connect the alligator clip of your test light to ground.
^ Do not depress the brake pedal.
^ Turn the ignition "on".
^ Push the tip of your tester into one wire and the tester should light.
^ Now test the other wire and again the tester should light.
^ Depress the brake pedal and re-test. Only one wire should now be hot.