Truck Brake Lights Not Working? Read How to Fix

The brake lights are an indispensable part of the vehicle. Are your truck brake lights not working? It can be aggravating to see the brake lights not light up even when you depress the brake pedal to its fullest extent. If you are wondering, “How can I check my brake lights by myself,” then you are at the right place.

Brake lights not working?

Driving with damaged brake lights can be extremely dangerous, compromising the safety of your vehicle. Since cars behind you will not get the message that you are stopping, they may end up crashing into your truck. If you need to solve the problem of your malfunctioning brake lights, read on to find out how to diagnose and fix them.

What Do Brake Lights Do?

The brake lights of your truck perform an important function. They signal to vehicles behind you that you are slowing down or stopping. Consequently, they can reduce their speed. They may also decide to change lanes and continue on their way.

use of brake lights during lane change

Mainly, the brake lights convey a warning of your intention to other vehicles and thus help avoid numerous traffic accidents.

Internal Working of The Brake Lights

What causes brake light failure? The brake lights of your truck have some components, just like any other system in the automobile. Faults in any of these fundamental parts can lead to your truck brake lights not working.

working citcuit of Brake lights

Brake Light Components

The brake light system in most vehicles is a simple circuit consisting of:

  • brake light switch
  • light bulbs or lamps
  • fuses
    automotive fuse to be checked if brake lights not working
  • connecting wires

The most commonly used type of brake light switch is mechanical. Usually mounted close to the brake pedal arm, it is triggered by depressing the pedal. Then the switch automatically closes to turn on the brake lights. Another type of switch is the hydraulic kind, which is operated by the pressure of the brake fluid in the pipes when the brake is applied.

hydraulic brake light switch

Diagnosing The Truck Brake Lights Not Working

As a driver, the safety of your passengers as well as yours is your primary concern. Stay safe by finding the cause of your faulty brake lights.

To check the faulty brake lights, you will need a digital multimeter or a voltage test light. You will also need another person as a helper.

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Voltage test light
Voltage Test Light

Steps To Check The Truck Brake Lights

Let the helper press down on the brake pedal while you look at the brake lights from behind the car. If you absolutely cannot arrange for a helper, you can use a pry bar of the correct length instead. Place the pry bar on the brake pedal and prop it against the seat. Move the seat forward until the brake pedal is fully depressed.

pry bar to operate the brake pedal

1. If The Bulb On Only One Side Is Not Working

Then it is likely to be a damaged bulb.

You can check the condition of all the bulbs by opening the tail light assembly and looking at the bulbs. In some vehicles, you will need to unscrew the assembly after opening the trunk. Check the video under replacing the light bulb for detailed steps. In other cases, the arrangement attaches by internal clips and can be popped out. While you are at it, also check the socket for any corrosion.

use of brake lights during lane change

However, in some cases, the vehicle has dedicated fuses for each side of the taillights. So, if the bulbs are okay, the next thing to check is the fuse for the stoplights. The following video contains detailed steps on how to diagnose your truck brake lights not working correctly.

2. If The Lower Brake Lights Are Haywire But The Third One Is Fine

It may be a burnt fuse. Most vehicles have one fuse for the lower stoplights and another for the third one. There is nothing to worry about since it is easy to replace the fuses of automobiles if you know what you are doing.

Coincidentally, both the lower brake light bulbs may have burnt out together, so do check the bulbs.

3. If All The Lights Are Dead

It is likely the brake light switch that is faulty. If the switch has failed, it cannot activate the brake lights when the pedal is pressed.

brake light switch

4. If The Lights Are Staying On All The Time

There is likely an internal short in the wiring. It will lead to the bulbs wearing out and burning faster. It is also a parasitic drain on the battery, besides conveying the wrong signal to other drivers.

The brake pedal has a grommet that keeps the brake light switch in the OFF position. If this grommet disintegrates and falls out, it could also cause the lights to stay ON constantly.

grommet on the brake pedal

How To Fix The Non-Functional Brake Lights?

Once you have identified the faulty component, it is time to replace it. Don’t worry, bulbs are very easy to replace.

1. Replacing The Brake Light Bulbs Or Sockets

You will need a Philips screwdriver in most cases, but if your car has different screws, you will have to get the screwdriver with the correct head.

You can procure the replacement bulbs either online or from brick and mortar automobile stores. The best option is to take the original bulb to the shop. They can provide you with the correct replacement.

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Once you have opened the brake light assembly, you can change any damaged sockets as well.

2. Changing The Brake Light Fuse

There are usually two or three fuses in the brake light system. One of them is the 15A fuse supplying power to the light bulbs located in the main fuse box under the hood. The second one is the 10A fuse supplying power to the brake light switch. You can find this one under the dash, in the driver’s foot space. Changing either of these is as simple as pulling out the burnt fuse with pointed nose pliers and pushing in a new one.

brake light fuse

How can you tell if a brake light fuse is bad?

By inspecting the fuse with the naked eye, you can spot any burnt or blown fuses. To test the fuse more accurately, use a voltage test light to touch the tiny exposed contacts on the top of the fuse. If the light glows on both sides of the fuse, it is functional, otherwise, it is not.

Note: Fuses do not burn out by themselves. A burnt fuse is likely the result of some other fault in the circuit. One place you should check is the electrical connections to your trailer for corrosion damage.

corrosion in the trailer wiring

There could also be a short somewhere in the socket, the wires or even the bulb casing.

3. Replacing The Brake Light Switch

The brake light switch is located just above the brake pedal. Reaching into the small space may require some gymnastics on your part unless you are a small person. You will need pointed nose pliers to take out the safety clip. Keep this small part safe. You can do the rest of the task by hand.

If your car has a hydraulic brake light switch, you will need to consult a mechanic for its repair or replacement.

4. In The Case Of Corrosion

If there is any corrosion in either the socket or the casing, and it is only a trivial amount, you can scrape it off with sandpaper or the end of your screwdriver. White vinegar or baking soda can remove the rust.

corroded bulb socket for faulty brake light

However, if a large amount of rust has formed such that the component is deformed, you need to replace it.

5. If The Wiring Is Faulty

Unfortunately, the wiring is somewhat complex and not easy to change at home. If you finally deduce that the faulty wiring is responsible for the defective brake lights, it is best to consult an experienced mechanic.

How Much Does It Cost To Fix Brake Lights?

A replacement bulb costs about USD 5 to 10. A new fuse costs too little to be sold singly. You can get around thirty to forty pieces for 2 USD. However, new brake light switches are somewhat more costly. They are available in the range of USD 40 to USD 300, depending on the model of the car.


In this manner, you can solve the problem with your truck brake lights not working. You can fix the problem yourself in almost all cases, provided you understand how the brake light system works. You can buy either OEM or aftermarket replacement parts in any automobile spare parts shop. Even online stores sell replacements nowadays. Remember to check your car’s manual to find out the compatible part.

If you require help in disassembling anything, you can talk to a mechanic from any local garage. Any friend of yours who knows about automobiles can help you out as well. If you were asking yourself “Can I change my own brake light,” your question has been answered.

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