It is both frustrating and unsafe if your brake lights are stuck on. The most common reason that they stay on is a brake light switch that has failed.
How Brake Lights Work
Brake lights work by having an electric current sent to the brake pedal switch at all times (even with the vehicle off). When you press the brake pedal in, it sends the current to the brake lights. It’s a very simple system that has not changed in almost a century.
Brake Lights Stuck on Causes
Here are the most common causes of brake lights that won’t turn off. Most of them are related to the switch that turns them on or off. They are written in order from most likely to least likely to be causing the problem.
1. Bad Brake Light Switch
Underneath the dashboard there is a switch that the brake pedal presses into. When you press the brakes this switch is activated and the brake lights turn on. When you take your foot off the brake, it presses this switch in and the brake lights turn off.
The inside of the brake light switch can wear out from the hundreds of thousands of times the brakes are pressed. When this happens the brakes can stay on. Replacing the brake light switch is far and away the number one thing that fixes brakes that are stuck on.
2. Brake Switch Adjustment
Nearly all brake switches have an adjustment built into them that allows them to to snug up to the brake pedal. If this adjustment is off, the plunger on the brake pedal switch will not press in all of the way. This keeps the brake lights perpetually on.
3. Weak Brake Pedal
If the brake pedal is closer to the floor than it should be, the plunger on the brake pedal switch will no longer be able to be pressed in all the way. This keeps the brakes lights on even when the switch is just fine.
To test whether or not this is the case, put your feet behind the brake pedal and pull it up. Did it turn the brake lights off? If it moved a lot higher it’s a sign that the pedal is softer than it needs to be. If it barely moved at all, but the brake lights did turn off, it probably still means that you need a new brake pedal switch. Or it could be just ever so slightly out of adjustment.
4. Wiring Issue
It is possible that a wiring harness issue has caused some of the wiring to melt together, or short out in some way. I’ve personally seen this, but it is a 1% of the time or less issue.
Diagnosis
The easiest way to diagnose brake lights that are stuck on is to unplug the wiring harness to the brake pedal switch. If the brake lights turn off, you know that the switch is bad. If the brake lights stay on, you’ll need to find the wiring problem.
Conclusion
Good luck diagnosing why your brake lights aren’t turning off. If there is anything that you might be able to add for the next person, your comment below is most welcome. Good luck!