When a vehicle's brake lights all go out at the same time, the culprit is usually the
"stoplight Switch" which is operated by depressing the brake pedal.
To replace a stoplight switch, first determine what type of switch you have.
If you have an electrical switch mounted to the brake pedal in the passenger compartment:
- Unscrew the switch.
- Unplug the wires.
- Replace with a new switch. Adjust as needed.
- Plug the wires back in.
If you have a hydraulic pressure switch that is mounted in the brake master cylinder:
- Mark and disconnect the wires.
- Unscrew the switch.
- Screw the replacement switch in.
- Reconnect the wires
Here's a picture of the "Stoplight Switch", aka Brake Light Switch - 1995 GMC K1500 Sierra
Brake lights (stoplights) are activated by a mechanical switch on the brake pedal.
To test a suspected bad stoplight switch, bypass it with a jumper
wire. The stoplights should light when the wires are connected. Use the
test light to see if there is power at one of the lights.
- If the lights come on when the wires are connected but not when the brakes are applied, replace the switch.
- If the stoplights operate without the key on, remove the stoplight fuse before removing the switch.
- If the new switch is adjustable, adjust it so that it is open when
the pedal is released.lights should come on about 1/4" after the
pedal is applied.
Brake lights should have power at all times on one side of brake switch.
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