Brake Light Switch Buyer's Guide
- Also called a brake relay, a modern brake light switch controls the power supply for the brake lights. It usually sits above the brake pedal, either beneath the dashboard or on the firewall near the pedal lever’s top.
- The brake light switch makes it possible for the brake lights to switch on when you step on the brake pedal. The switch also informs the vehicle computer and other relevant systems that the brakes have engaged.
- As various systems intertwine closer for the sake of efficiency and convenience, more and more electronics look to the brake light switch for their cue on when they should run.
- Symptoms of a bad or failing brake light switch include erratic brake lights; the transmission shifter keeping the car in the Parking gear; the cruise control system staying activated; an illuminated brake warning light, Check Engine Light, and/or ABS System Warning Light; and problems in vehicle systems that rely on the brake light switch.
- A replacement part for a bad or failing brake light switch can cost anywhere between at least $3 up to around $105.
When you hit the brakes of your car, its brake lights switch on to warn other drivers on the road about your maneuver. The current required by those exterior lights passes through the brake light switch, a small but important electrical relay that controls the power supply to the brake light assemblies.
What is a brake light switch?
Also called a brake relay, a modern brake light switch controls the power supply for the brake lights. It allows a control circuit with lower voltage to operate the switch despite the disparity in voltage.
This mechanical switch forms a critical part of the brake pedal assembly. It usually sits above the brake pedal, either beneath the dashboard or on the firewall near the pedal lever’s top—places that a mechanic or technician can easily access for replacement.
Stepping on the brake pedal not only activates the brakes but also triggers the brake light switch to close the circuit leading to the brake lights. An electric current can flow through the completed circuit to power the exterior lights.
Vehicles built during the 1960s or earlier relied on the brake line’s hydraulic pressure to activate the brake lights. These hydraulic-based switches suffered severe reliability issues, so car manufacturers eventually adopted more rugged mechanical switches.
Modern-day brake light switches last much longer and enjoy exceptional reliability, although they can fail earlier than expected. When the switch in your car fails, you must replace it as soon as possible.
What does the brake light switch do?
The brake light switch makes it possible for the brake lights to switch on when you step on the brake pedal. Conversely, it turns off the lights once you let off the pressure on the pedal.
The switch also lets the vehicle computer know that the brakes have engaged. It sends a signal to other relevant systems like the transmission shifter, which we’ll cover in detail shortly.
Why is a brake light switch important?
The brakes and its associated parts, including the brake lights and the brake light switch, keep you safe on the road. The brakes stop your car while the switch lets the lights warn the drivers behind you about your intentions.
You may also find it surprising how many seemingly unrelated vehicle systems depend on the brake light switch. As various systems intertwine closer for the sake of efficiency and convenience, more and more electronics look to the brake light switch for their cue on when they should run. These include anti-lock braking, cruise control, push-button start, and transmission shift systems.
How do you know if your brake light switch is bad?
Symptoms of a bad or failing brake light switch include:
Erratic brake lights
When the brake light switch goes bad or suffers a failure, the brake lights that depend on it for power will behave abnormally. Oftentimes, the lights may flicker, generate less illumination, or even refuse to work because of the intermittent or nonexistent power supply.
Sometimes, the brake lights will activate, only to stay lit. Other times, the lights will turn on even if you keep your foot off the brake pedal.
Transmission shifter keeps the car in the Parking gear
The transmission shifter lets you change the gears of your car. As a safety measure, most vehicles will not shift out of the Parking gear until the brake light switch confirms the brakes have engaged.
A faulty brake light switch cannot send that signal. The transmission shifter keeps the vehicle in Parking gear until you resolve the problem by replacing the switch.
Cruise control system keeps running
Some vehicles come with cruise control systems that take over the car’s throttle system and keep it at a specific speed. The brake light switch turns off this automatic speed control system to help bring the car to a stop.
Understandably, if the switch goes bad or fails, it won’t deactivate cruise control. You’ll have to manually turn it off, which can prove distracting and dangerous during the high speeds mandated on a highway.
Illuminated brake warning light
This dashboard-mounted warning light keeps you appraised about the state of the vehicle’s brakes. It can also trigger when the brake light switch wears out or breaks down.
Activated Check Engine Light and ABS System Warning Light
While these warning lights usually concern themselves with other problems, they can come to life if the brake light switch gets stuck in either a closed or open position. They may also activate if the switch only works every now and then instead of running every time you step on the brake pedal.
Problems in vehicle systems that rely on the brake light switch
Other vehicle systems that rely on the brake light switch may stop working properly when the switch goes bad. In a car with a push-button start system, a bad or failing brake light switch may prevent the engine from starting up.
How much does a replacement brake light switch cost?
A replacement part for a bad or failing brake light switch can cost anywhere between at least $3 up to around $105. Often sold individually, these parts can also come in a set of two and as part of a kit.
The price tag of a brake light switch depends on factors like the part’s manufacturer, the quantity sold, and the vehicle’s make and model. Original Equipment Manufacturer (OEM) parts cost more because of their exclusivity to official dealerships and chosen retailers.
Selecting a brake light switch replacement
There isn’t any universal fit brake light switch because the relay device can vary between vehicle makes and models. You cannot replace a broken or worn Mercedes Benz W210 brake light switch with a Honda Accord brake light switch, and vice versa. You’ll need to find a compatible replacement part for your vehicle’s switch.
To help you pick the best brake light switch for your ride, our online shop comes with a filter bar. Entering your vehicle’s year, make, and model will quickly bring up a guaranteed fit replacement part from our catalog.
A DIYer's Guide: Replacing Brake Light Switch
Whenever you step on the brake pedal, you're not just engaging your brakes, you're also activating a switch that lights up the brake lights at the rear of your vehicle and warns motorists behind you that you're slowing down. Not only that, your brake light switch is also responsible for disengaging your vehicle's cruise control system every time you depress the brake pedal. A damaged or defective brake light switch can spell disaster for you and your family. If you find nothing wrong with your brake light bulbs yet they refuse to light up when you press the brakes, you should replace your brake light switch right away. Fortunately, doing so is a job you can easily do yourself.
Difficulty level: Easy
Here's what you'll need:
- Wrench and socket set
- Phillips screwdriver
- Replacement brake light switch
- Vehicle owner manual
Step 1: Open the driver door of your car and locate the brake light switch underneath the dashboard, near the top of your brake pedal. Usually, the brake light switch is attached to a small bracket that holds it in position.
Step 2: Check if your brake light switch is out of position and if its electrical connection is securely attached. It's possible the switch could just be stuck in the "on" or "off" position.
Step 3: After verifying that the brake light switch itself is defective, use your Phillips screwdriver to remove the screws holding the electrical cover in place behind your brake pedal.
Step 4: Remove the electrical cover. Use your socket wrench to remove the bolts holding the brake light switch in place.
Step 5: Remove your brake light switch and disconnect all electrical attachments.
Step 6: Install your new brake light switch by plugging the electrical connector into it and using the same bolts you removed eariler to secure your brake light switch in place.
Step 7: Screw the eletrical cover back into place. Test your new brake light switch by pressing your brake pedal. If you're alone and have difficulty seeing your brake lights, turn the ignition key to the "ON" position, shift to reverse, engage the parking brake, then step out of your vehicle and come around back for a look.