Symptoms of a Bad Brake Light Switch

Pressing the brake pedal causes your vehicle to decelerate or stay in a stopped position. And while you’re holding your foot on the brake, the brake lights are illuminated. The connection between the brake lights and pressing the pedal is the brake light switch.

Typically mounted in the vicinity of the firewall behind the brake pedal lever in the driver’s footwell or near the pivot point under the dash, it’s a simple switch with an on and off position. The brake light switch, also called a stoplight switch, can fail from constant use while you’re driving, and it can affect more than just whether your brake lights come on. The part for most vehicles ranges between $10 and $70, but some can be more than twice that amount for unique designs.

What contributes to a brake light switch failure, and how do you know when it’s bad? Here are common brake light switch symptoms, how to check the switch, and what you need to do to replace it.

What Causes a Bad Brake Light Switch?

A bad brake light switch is typically caused by wear or damage to the switch itself, the wiring or connectors leading to the switch or the brake pedal mechanism that activates the switch. Over time, the switch can become worn or damaged due to regular use and exposure to moisture and dirt in the footwell. Imagine how many times you press the brake pedal for every mile you travel in stop-and-go traffic, and what that means for times the brake light switch operates.

Additionally, if the brake pedal is not adjusted properly, it can cause stress on the brake light switch, leading to premature wear. In some cases, electrical issues or problems with the brake light circuit can also cause issues with the brake light switch, such as a blown fuse or a faulty relay.

Symptoms of a Bad Brake Light Switch

If you have a bad brake light switch, symptoms can vary depending on your vehicle. However, two of the most prevalent and common are that the brake lights stay on all the time if the switch fails in the closed position, or the brake lights won’t illuminate at all when the pedal is pressed, indicating a failure in the open position.

These symptoms aren’t exhaustive, though. Other potential concerns can include:

  • The cruise control won’t set or it cancels unexpectedly
  • Brake lights flickering or activating intermittently
  • The shift interlock won’t disengage, and you can’t move the gearshift lever normally or it might be stuck in park
  • An ABS light illuminated

Some redundant switches – a secondary switch that’s either integrated or altogether separate – can confuse you with the symptoms. For example, you might not be able to set your cruise control but the brake lights illuminate normally.

How to Diagnose a Bad Brake Light Switch

If you suspect that you have a bad brake light switch, here are a few diagnostic steps you can take:

  • Watch the brake lights. Normally, the simplest way to check whether or not your brake light switch is working is to observe the brake lights when you apply the brakes. If the brake lights don’t come on or work intermittently, there’s a good chance the brake light switch is faulty.
  • Check the fuse. A blown brake light fuse can also cause the brake lights to fail, so check the fuse box to make sure the fuse hasn’t blown.
  • Remove the brake light switch. You can remove the switch and check for signs of damage or wear. Look for any cracks, melted plastic, or frayed wires. It’s also a good idea to clean the switch with a wire brush and reconnect it to see if that fixes the problem.
  • Use a multimeter.  If you have a multimeter, you can use it to test the continuity of the brake light switch. First, disconnect the switch and set the multimeter to the continuity setting. Then, touch the leads of the multimeter to the two terminals on the switch. Press the switch. If there’s continuity when it’s pressed and it stops when the switch is released, the switch is working properly.
  • Test the power supply. You can also use a test light to check whether the brake light switch is getting power or not. With the ignition on and the brake pedal pressed, connect the test light to the negative terminal on the battery and then touch the other end to one of the wires on the brake light switch. If the test light doesn’t light up, there’s a problem with the power supply to the brake light switch.

If any of these tests indicate a problem with the brake light switch, it will need to be replaced. It’s important to consult your service manual or a professional mechanic if you’re unsure of how to replace the brake light switch on your specific vehicle or if any issues arise during the replacement process.

At an AutoZone near you, find your new brake light switch and any tools you need to diagnose and replace it. If you decide that it’s too big a job to tackle on your own, let AutoZone help you find qualified professional mechanics through our Shop Referral Program. 

FAQ/People Also Ask

What are the symptoms of a bad brake pedal position sensor?

Commonly, your brake lights won’t activate or they will stick on all the time. Your cruise control might not function, and it’s possible you could have trouble moving the gearshift lever.

How do I know if my brake light switch is bad?

It’s relatively simple to test the brake light switch. Check for continuity with a multimeter or a circuit tester light.

Can the brake light switch affect shifting?

Yes, it can. Since vehicles with an automatic transmission need to ‘see’ that the brake pedal is pushed to shift out of park or from drive to reverse or back into park, a faulty brake light switch can prevent your car from shifting properly.

How do you test a brake light switch?

An easy method is to check for power with a test light at the switch, then test for power when the switch is pressed and the circuit is closed.

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