If your car's brake lights stay on even when the engine is off, the brake light switch -- a small, innocuous electrical part you'd only see once something goes wrong with it -- is likely the culprit. It could happen suddenly and without warning, and you'll most likely end up with a weak or defective battery if it's left unattended. The result? The battery won't have enough juice to turn the starter, leaving you stranded. Even the best car batteries won't stand a chance, especially older cars with halogen bulbs that suck out more power.
You'll find the brake light switch -- also called the stoplight switch -- behind the brake pedal, near the driver's footwell. It's exactly what it sounds like: a switch that activates the rear brake lights. Depending on your vehicle's make and model, it may work mechanically when you step on the brake pedal, or it may respond to changes in pressure as part of a hydraulic system. No matter which, a bad or faulty brake light switch is bad news, and you'll need to be aware if it breaks to avoid more costly problems.
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Symptoms Of A Bad Brake Light Switch
I've owned a car that kept the brake lights on (even when the engine was off) when the brake light switch conked out. And another car I owned had no brake lights despite my pushing the pedal. However, there are other symptoms of a failing or broken brake light switch besides lights that refuse to turn on or remain off.
Flickering brake lights could be hard to notice when you're behind the wheel, but cars in back of you won't likely appreciate the light show. In other vehicles, the ABS light might illuminate, while the cruise control might not work in still others. Finally, the brake light switch might affect the shifting behavior of the gearbox, particularly in cars with an automatic transmission. It won't destroy the transmission like towing heavy loads that are beyond your vehicle's capacity, but it could affect acceleration and fuel economy.
Factors that might cause the brake pedal switch to fail include age, wear and tear, or electrical issues such as relay problems or blown fuses. Older cars are at a higher risk of having brake switch issues, since moisture, dust, heat, and extreme cold can lead to early deterioration of electrical parts.
What Other Issues Can Cause My Brake Lights To Stay On?
In most cases, the brake light switch is to blame if the brake lights remain on, but there are other reasons to consider. A stuck brake pedal, which most likely signifies problems with the brake booster or vacuum pump, may cause the brake lights to remain on, especially if the pedal stays down. Or a wonky pedal spring may be to blame — it's the spring that enables the brake pedal to rise after pressing it. If the spring wears out or is stuck, it may cause the brake lights to remain on.
Finally, installing the wrong set of tail lamp bulbs can short-circuit the system, and it could happen if you wrongly swapped out double-contact bulbs for single-contact ones. Brake lights require double-contact bulbs that light up when activating the parking lights and glow brighter when applying the brakes.
If the problem is a faulty brake light switch, a new one will set you back anywhere from $10 to upward of $100 or more, depending on your car's make and model. But if you're not sure what's wrong, we highly suggest consulting a professional mechanic to get to the root of the issue the first time around.
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