Brake Light System Repair

Got a brake light out? Anyone that drives a car should know how to do minor repairs using everyday tools without going to a garage. In this guide we will show you how to replace and repair your brake bulb system by testing the light socket, fuse, wiring, switch and BCM. By following this guide you will have the satisfaction of fixing it yourself and save a considerable amount of money in the process.

When replacing vehicle bulbs use high quality replacement parts to ensure proper operation and a longer lifespan of the repair. Cheaply made bulbs tend to burn out more rapidly which requires a repeat replacement.

After testing you may need a replacement bulb or socket and basic tools you can get from Amazon or the local parts store when you are ready to begin.

There are basically two styles of bulb replacements which are; The brake lens needs to be removed to access the bulb, or the bulb socket can be removed by simply twisting it counterclockwise from the backside of the lens either through an access hole which is covered by a small plastic panel, or through the trunk, lift back or hatch. We will show you both types and how to test the system in the following guide.

Let's Begin

Tools and supplies that maybe needed

Before starting park the car on level ground with the emergency brake on.

Checking and Replacing the Bulbs

Have a helper step on the brake pedal to confirm which brake bulb is out; right, left or high center lights. If none of the lights are working then the bulb is probably not the problem, though I have seen where all of the bulbs are out simply because they had gone bad one at a time. When you see a person who has a stop light out you should do the right thing and tell them, this helps prevent accidents. If all bulbs are okay and the system is not working then continue with this guide past the bulb replacement section.

To begin you must determine which style of bulb replacement your vehicle has, this is done by inspecting the lens and looking for mounting screws which hold the lens to the vehicle that can be on the side of the lens. You may need to open the trunk, hatch back, tailgate or lift back.

If no mounting bolts are found on the outside of the lens they will be located in the back of the rear body panel. You may need to pull back the truck liner or remove a few plastic trim pieces before these nuts or the bulb socket is accessible. If no access hole is available you must remove the mounting bolts and remove the lens to gain access to the bulb. In the case below an access hole was provided by the manufacturer which makes the job a little easier.

This is what it looks like when the lens is removed.

Now that you have located the light socket and wiring harness its ready to be removed for testing or repair. On most American made cars and trucks this bulb has two jobs, both for the brake light and the blinker indicator which will have three wires feeding the socket; brake, turn signal, and ground wire. On European and Japanese cars this job is handled separately which will have just two wires, brake light power and ground.

Grasp the bulb socket and twist firmly counterclockwise, this will allow the socket to come loose from the lens. Sometimes they can be a little stuck in which case you can use a pair of pliers to help break it loose. 

Once the socket has been removed it will expose the bulb which may have a burned mark or be a light blue color which indicates a leak in the glass, in either case the bulb is no good.

Grasp the bad bulb and pull it from the light socket (some bulbs you will need to push down and twist counterclockwise) then match it to the new unit, they should by identical. Plug the new bulb in and have a helper push the brake pedal to see if it works, if it does reinstall it back into the lens and reassemble the plastic cover or trunk liner and you are all set. If the light is still not working after replacing the bulb or its dull or dim then more repairs are needed, continue with the guide.

Testing the Bulb Socket

This is where some testing is needed to repair a bad connection or broken wire. Start with a test light and secure the ground clip to a known good ground source such as a bolt or solid metal piece. It's important to get a good connection free from rust or paint because the test light depends on this conductivity to work correctly while giving you a good test result. Wiggle the clip so the teeth of the spring loaded clip dig into the metal to ensure a good connection.

Have a helper hold down on the brake pedal, the remaining working brakes lights should be on. Use a test light to probe each of the brake light sockets feed wires; one of them should light up. If you cannot find power then access the opposite light that is working and probe the wires until power is found to confirm the test light is working. If power is present at the socket and the light is still not working continue with the guide. If power cannot be found skip down to: "Testing the Brake Light System" in this guide.

If you have power at the socket the next step is to check the system ground. Attach a pointed metal object such as a scribe to the test light clip and probe the brake light feed wire and the ground wire of the socket, if the tester lights up the circuit is working and the fault is in the bulb socket connections. If the test light does not light up there is an open connection in the ground wire. A bad ground will make the bulb be dim, dull or not work at all; if the connections are loose the bulb will flicker. A loose connection can be fixed by enhancing the spring tension on the socket terminals.

You can either make a new ground wire connection by cutting the wire and making a new ground wire to any metal part near the socket, or follow the wiring harness and look for obvious damage or cuts in the wiring and repair as needed.

Next, remove the bulb socket and inspect the electrical connector for burned or melted terminals, this is caused by high resistance creating an open connection causing the bulb not to work. If damaged or melted, the connector with pigtail wires will need to be replaced which you can get from Amazon or from the dealer for about $35.00 bucks. With the foot off of the brake pedal cut the harness and splice in the new connector.

Next, inspect the bulb socket; many times this socket will be subject to heat and corrosion. Manufacturers will install dielectric grease into the socket to help protect the connection, but with time this clear or brown grease will melt out and expose the connectors to the atmosphere causing rust or corrosion creating an open connection. Use a sharp object such as an Exacto knife to scrape the connection clean. This with help the bulb terminals connect to the socket allowing the bulb to work again, if this socket is badly damaged it should be replaced.

With all connections cleaned or socket replaced and the power and ground checked with any repairs made to the wiring or connections reassemble the socket and bulb onto the wiring harness. Have a helper step on the brake pedal to confirm the bulb operation. Then reinstall the bulb socket back into the lens and reinstall the lens if needed and you are all set.

Watch this video that gives you an idea of what you are in for when replacing a bulb before you begin. Then follow down the guide to learn what to look for when none of the lights are working.

Testing the Brake Light System

If no power can be found in the brake light system then the problem is further down in the electrical circuit. 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.

Reasons for lack of system power

  • Blown brake light fuse
  • Broken wire in the harness
  • Body control module BCM failure
  • Turn signal or multi function switch failure
  • Brake light switch failure

Begin by using a test light to check the brake light system fuse in the fuse panel which can be identify by the owners manual or on the lid of the panel. Replace the fuse if it's blown, this could be caused by a shorted wire to ground, a melted socket or a weak fuse. If the fuse is okay continue down the guide.

This is an example of melted terminals on the bulb.

Next in the process is the brake light switch which completes the circuit when the pedal is depressed by the driver. Locate the switch near the upper part of the pedal; it will have wiring connected to it. This switch simply connects the circuit once the pedal is depressed connecting power to the lighting system which are on vehicles using a BCM or lighting module which uses a ground trigger that is monitored by the body or lighting control module which in turn powers the brake lights.

Begin by inspecting the wiring harness, look for obvious damage such as a cut, wear mark or broken wire indicating the harness has rubbed against a metal frame causing the failure. Wiggle the wiring while pressing the brake pedal down to see if you can get the lights working, this would indicate an internal broken wire. If everything looks okay use a test light or voltmeter and get a wiring diagram from an online repair manual such as Mitchell1 or search Google Images.

Using the diagram to test for power or ground (depending on the vehicle) entering the switch on the connector side, then reinstall the connector to the switch and test through it. If no connection is made the switch is bad and needs replacement, this is a common failure.

On American vehicles the brake light circuit is routed through the turn signal switch which can go bad not allowing the currant flow to continue to the brake lights. Using the wiring diagram test the color wires that are ingoing and outgoing to see if the circuit is working, if not replace the switch, this is sometimes called a multifunction switch.

Learn More: Turn signal switch replacement

On vehicles using a lighting or BCM module use a wiring diagram to test the ingoing signal from the switch and the outgoing voltage output to the lights. If no outgoing signal is found and the remainder of the lights is working the module is bad and replacement is required. If none of the lights are working check the fuse for the BCM or lighting module.

If a brake light flickers it's because the power or ground is being obstructed momentarily. The most common cause for this is a loose fitting bulb socket, while a helper holds down on 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.

A brake light system in most cases is a basic electrical system involving a simple positive and ground connection controlled by a switch which rests in the open position and then 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.

Check out our brake light bulb repair forum where our online mechanics have answered thousands of your questions.

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