What Is a Brake Light Switch and When Should You Replace It?

Updated: Nov. 28, 2022

The brake light switch on your vehicle serves an important safety function. Learn how to test it and determine when to replace it.

When you press your vehicle’s brake pedal, the brake light switch is what supplies power to the signal lights at the back of your vehicle to warn other drivers you have slowed.

Where is a brake light switch located?

As part of the brake-pedal assembly, you can find this switch under the dashboard or on the firewall near the top of the pedal lever. Replacing one is easy, and sometimes it has to be done for safety, similar to how never ignoring these car sounds is crucial for car safety.

The switch was once driven by hydraulic pressure in the brake line (a system prone to failure). Vehicle manufacturers transitioned to the more reliable mechanical brake light switch by the end of the 1960s. Now, it is rare for a switch to fail. Current designs employ a relay, allowing a lower-voltage control circuit to operate the main power supply switch for the brake lights. This configuration creates a reliable switching mechanism with a long lifespan.

Diagnosing the problem

How do you know if your brake light switch is bad? You won’t get much warning before a brake light switch fails; possibly some flickering or inconsistency in light stability. Most likely, the brake lights just stop working.

Chances are someone else has alerted you to the issue. Check for yourself at night. Looking through your side mirror, light intensity should increase behind the vehicle as you engage the brake. Alternatively, you can back up to a wall or garage door, put the car in park, and watch through the rearview mirror as you engage the brake. Watch out for these things you’re doing to your car that car mechanics would never do.

Broken brake light?

Identify a faulty brake light switch through a process of elimination. Check the light bulbs for cracks or broken filaments. Make sure the bulbs and wiring harnesses are connected and seated tightly. Did both lights fail at the same time? If so, a bad switch is more likely.

How much does it cost to replace the brake light switch?

A replacement brake light switch generally costs around $30 to $75, depending on the make and model of the vehicle. Getting a brake light switch fixed at a shop will add typically $80 to the repair.

Learn the things you should never do to your car in the video below.

The Family Handyman
Originally Published on The Family Handyman