Brake Light Not Working? Here's How to Fix It

How Brake Lights Work

When you step on the brake pedal, a switch at the top of the pedal arm closes a circuit. That sends power through a fuse, down the wiring harness, and to the brake light bulbs in your tail light housings. On most vehicles, you've got three brake lights: left, right, and the center high-mount stop lamp (CHMSL) on the rear window or trunk lid.

The circuit is simple, which means diagnosing the problem is usually straightforward. There are only a few parts that can fail.

Start Here: Quick Diagnosis

The fastest way to narrow it down is to figure out which lights are affected.

Only One Brake Light Is Out

If one brake light is dead but the others work, it's almost certainly the bulb. All three brake lights share the same switch and fuse. A bad switch or blown fuse would kill all of them at once. Pull the bulb from the dead side and check the filament. If it's broken or the glass looks dark, swap in a new one. Five minute job.

All Brake Lights Are Out

When every brake light goes dead, including the center one, the problem is upstream. The most common culprit is the brake light switch on the pedal. A blown fuse is the second most likely cause. It's very unlikely that all three bulbs burned out at the same time.

Brake Lights Stay On All the Time

This is the opposite problem, but it's related. If your brake lights won't turn off, check the brake pedal for a missing bumper. There's a small rubber or plastic stop that pushes against the brake light switch when you take your foot off the pedal. If it falls off or crumbles (they're made of cheap material that degrades over time), the switch stays engaged and the brake lights stay lit. You can find a replacement bumper at any parts store for a couple of dollars.

How to Check Each Part of the Circuit

1. Check the Bulbs

Start here even if all the lights are out. Access the bulb from inside the trunk or behind an access panel in the tail light area. Twist the socket counterclockwise, pull it out, and inspect the bulb. Many vehicles use a dual-filament bulb (like a 3157 or 1157) that handles both the tail light and brake light. The brake light uses the thicker filament. It's possible for one filament to burn out while the other still works.

If you're not sure whether the bulb is good, test it with a multimeter or just swap in a new one. They're cheap enough that it's worth doing as a first step.

2. Check the Fuse

Find your fuse box (usually under the dashboard on the driver's side or under the hood). Look for a fuse labeled "stop," "stop lamp," "brake," or "STP." Pull it out and look at the metal strip inside. If it's broken, replace it with one of the same amperage rating.

If the new fuse blows as soon as you hit the brakes, there's a short circuit somewhere. Don't keep replacing fuses. You need to find the short first, or you risk melting wiring.

3. Check the Brake Light Switch

The brake light switch is mounted at the top of the brake pedal, under the dashboard. You can usually see it by looking up under the steering column. It's a small plastic switch with a wiring connector plugged into it.

To test it, have someone press the brake pedal while you check for voltage at the switch connector with a multimeter or test light. You should see 12 volts on one terminal with the pedal released, and 12 volts on the output terminal when the pedal is pressed. If you get power in but nothing out when the pedal is pressed, the switch is bad.

Replacing the switch is usually a 15-minute job. Most are held in by a clip or a twist-lock mount. No special tools needed.

4. Check the Wiring and Grounds

Wiring issues are less common but worth checking if everything else looks good. Inspect the wiring harness between the brake light switch and the tail light housings. Look for damaged, pinched, or corroded wires, especially where the harness passes through the body into the trunk area. Check the ground connections at each tail light. A bad ground is a sneaky cause of brake light problems. Clean the ground point down to bare metal, reconnect, and test again.

When You Need a New Tail Light Assembly

Sometimes the problem is the tail light housing itself. Here are signs you need a replacement:

• The bulb socket is melted, warped, or corroded beyond cleaning
• The housing is cracked and water has gotten inside
• The socket won't hold the bulb firmly and it flickers or falls out
• The internal wiring or circuit board is damaged (common on LED tail lights)
• You can see burn marks or discoloration inside the housing around the socket

Aftermarket tail light assemblies run $30 to $150 for most vehicles. You get a complete housing with fresh sockets, lenses, and reflectors. On most cars, the brake light, turn signal, and running light all share the same housing, so you'll be replacing everything in one shot. Installation is usually two or three bolts and a wiring connector.

Tips to Prevent Future Problems