Brake Light System Repair

Easy step by step repair guide on how to fix automotive brake lights, all lights out or a bulb that is dull or flickering, this article pertains to most non-LED lighting systems.

Difficulty Scale: 4 of 10

Tools and Supplies Needed

  • Test light or voltmeter
  • Sandpaper
  • Safety eyewear and gloves
  • Small screwdriver set
Begin with the vehicle on level ground, parking brake set while in park using a basic set of tools while wearing protective eyewear and gloves.

If a singular brake light bulb has failed visit - Brake light bulb replacement, if you have replaced the bulb and its still not working, is dull or flickers, or more than one bulb is out you're in the right place.

New Brake Light Bulb

All Brake Lights Out

Step 1 - If the system brake light fuse has failed the brake lights will not operate. Visit - Fuse test

Replace Brake Light System Fuse

Step 2 - When a brake light switch fails it will cause the brake lights not to operate, with the key in the "ON" position, use a test light and a wiring diagram to check for incoming and outgoing power. If power is present with no outgoing power while the pedal depressed, the switch has failed. Visit - Test Light Instruction

Test Light

Step 3 -  American vehicles incorporate the turn signal switch into the brake lights, when this switch fails it can cause both or one lower brake light not to work, access the switch wiring harness using a wiring diagram and test light to confirm the failure.

Turn Signal Switch

Step 4 - Some vehicles are designed with a lighting control module which can malfunction causing both lower or the center brake light to not work. Using a wiring diagram and test light check the incoming power feed from the brake light switch, if incoming power and trigger signal from the brake light switch is present without outgoing power to the brake lights, replace the lighting control module.

Dim or Not Working

Step 1 - Remove the bulb in question and confirm the correct unit has been installed, next turn the ignition key to the "ON" position and have a helper depress the brake pedal and hold. Using a grounded test light carefully probe the socket terminals/wiring, one should have power. If no power is present and the other two bulbs are operating the wiring has failed to that particular bulb socket.

Step 2 - If the bulb socket ground has failed the bulb will not work, using a pick or other small object clamp it to the test light and use the power which you just tested for to check the ground circuit, if the test light doesn't light up, the ground circuit is bad.

Test Ground

Step 3 - A brake light flickers because the power or ground is being obstructed momentarily, the most common cause for this is a loose fitting bulb socket. Remove the bulb in question, while a helper holds down the brake pedal move the bulb around slightly in the socket, if the bulb flickers replace or repair the socket as needed, also wiggle the wiring.

Helpful Information

Most American cars are designed with the lower brake light circuit wiring incorporated into the turn signal switch where the brake light bulb and the turn signal bulb are one and the same, the turn signal switch interrupts the brake light circuit and installs the blinker circuit when the switch is activated. Japanese and European auto makers design separate brake and turn signal electrical systems.

A brake light system in most cases is a basic electrical system involving a simple positive and ground system controlled by a switch which rests in the open position and closes (electrical contacts connected) when the pedal is depressed.

A brake lens and socket can melt and distort when the brake lights are kept on for an extended amount of time, avoid allowing the brake light to stay on overnight.

Best Practices

  • Replace brake light bulbs with manufacturers recommend replacements.


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published