Brake Switch
- Turn on the ignition switch, the main switch, and apply brakes. If brake light doesn't go on, check the brake light switch. If switch is defective, replace. If switch is okay, brake light is defective.
- If brake light goes on, connect the positive probe to terminal 12 of control unit connector and negative probe to terminal 9 with brakes applied. See Figure. If there is no voltage, there is an open circuit in wiring harness.
- If there is 12 volts, connect positive probe to terminal 8 and negative to terminal 9 of control unit connector. Apply and release brake pedal and measure voltage. With the brakes applied, there should be 12 volts. With brakes released, there should be no voltage.
- If voltages test out okay in step 3, switch and circuits are okay. If not, connect positive probe to terminal 25 of brake light switch connector and negative to ground. See Fig 1. Measure voltage. If there is no voltage, there is an open circuit in the wiring harness.
Connector is viewed from wire side.
- If there is 12 volts, disconnect the brake switch connector and check for continuity between terminals A and B. With the brakes applied, there should be continuity. With brakes released there should be no continuity.
- If continuity does not test out as specified, there is an open circuit in wiring harness from switch to control unit. If continuity tests out okay, remove and test the brake switch. Replace switch if defective.