Brake or tail light is not working: repair options and cost

Brake light is not working Left brake light is out.
Have any of your brake lights or tail lights stopped working? One burnt-out bulb may not seem like a big deal, however each of your taillights serve an important safety function. According to the NHTSA statistics, one-third of all car crashes in the US in 2017 were rear-end collisions1. This means that keeping all of your lights in working order can save you more than a warning or ticket from the police.
What are the repair options if your vehicle is out of warranty and a brake light or tail light is out?

If more than one light is not working, it could be a problem with the electric circuit, read more below. If one of the lights is not working, the first question is: Is it a regular bulb or LED light? Many modern cars use LEDs or light emitting diodes in the taillights and other exterior lights.
LED and conventional brake (tail) lights LED and conventional brake (tail) lights.
If it's hard to tell whether it's a bulb or LED, check the owner's manual for your car; you can find the information about the bulbs under 'Maintenance' or 'Specifications'.
LEDs are brighter, more efficient and have shorter response time, which means that other drivers will see them sooner. They are also supposed to last longer, but there is one drawback: in most cars, LEDs come with the taillight assembly as one unit and cannot be replaced separately. Do LEDs fail? Yes, contrary to what marketers want you to believe, there is no fail-proof technology. LEDs do go bad, although not as often as regular bulbs.

If some LEDs remain dark, while others work, like in this photo below, we know that the whole assembly is bad and must be replaced.
Bad LEDs in the brake lightBad LEDs in the brake light.
In this car, it's the left taillight assembly. Read more: Taillight assembly: part options and replacement costs.

If an LED light assembly is not working at all it makes sense to have it diagnosed first, to make sure that it's not the problem with wiring or the connector. We have seen many cases where one of the lights stops working because of the corrosion in the connector or other issue. This problem is more common for the third brake light; read more below.

If your car has regular bulbs, they are cheaper and easier to replace. If you are not comfortable changing the bulb yourself, you can take your car to a local dealer or any auto repair shop.
Rear tail lightsBrake and other lights at the back of the car. Honda Accord. See how this taillight looks from the inside.
Replacing one brake or tail light bulb in an average car will cost $10-$55 labor plus the cost of the bulb ($1-$7). In some cars it's very easy to do; in others the taillight assembly might need to be removed in order to replace a bulb. If you want to replace the bulb yourself, the key is to use the right bulb type and install it properly to avoid electrical issues.

In some cars, one bulb may be used for two functions; for example, work as a brake light and tail light (double-filament bulb). Often one filament fails while the other still works; see this photo of a good and burnt-out double filament bulb. This could cause, for example, one of the brake lights to stop working, while the tail light (of the same bulb) still functions.

Once you know which bulb is not working, you need to find out the bulb type. All cars use standard bulb types. For example, the brake light bulb in this white Honda is a double-filament 12 V - 21/5 W bulb, according to the owner's manual (you can find it under "Specifications"). The type of bulb is printed on the bulb. The brake/tail light bulb is W21/5W. The turn signal bulb is WY21W.
Removing the taillight bulb The owner's manual for this Honda says: Remove the socket by turning it one-quarter turn counterclockwise. Pull the bulb straight out of its socket. Push the new bulb straight into the socket until it bottoms.
Most auto parts stores carry these and other common bulb types.

You can find the instructions on how to replace a bulb in the owner's manual for your car that you can download from the car manufacturers website. In many cars tail light bulbs are removed by first turning the socket counterclockwise to open and then pulling the bulb out. If you want to be sure to install the new bulb the same way, mark the position of the bulb with a marker or snap a photo before removing it. In some cars, bulbs are installed on the board that is attached to the taillight assembly.

How to check if the bulb is good? In most cases it's easy to see when a bulb is burned out.
Checking a light bulb in a carThis bulb is good.
See this photo of a burned out and new license plate bulbs. If the bulb doesn't appear burned out, another way to check it is to measure the resistance of the bulb using a multimeter. A good bulb should have resistance from 0 to 3 Ohms. If the multimeter shows OL, which means the resistance is out of range (no continuity), the bulb is bad. Another way is to check the bulb using a 12V power source or as in this photo, a 9V battery. If the bulb has two filaments, they have to be tested separately.

Whenever you change a light bulb in the car,
Good and melted brake light bulb socketThe bulb socket on the left image is melted and must be replaced.
or if the new bulb doesn't work, check the socket that holds the bulb; see the photo. Often the light doesn't work because the bulb socket is melted or burned out. In this case, the bulb socket will need to be replaced. If your local parts store doesn't have it, you can order it from a dealer. A bulb socket costs from $5 to $15. In some cars, the socket comes as part of the taillight wiring harness. In this case, it may cost from $15 to $35.

How long do bulbs last in a car? In some cars, bulbs can last up to 10-15 years, although in other cars, bulbs are known to fail much earlier. It depends on where the bulb is installed, the quality of the bulb and many other factors.

What can cause the third brake light not to work? As with any light, it could just be a bad bulb(s) or LED unit.
Third brake light is not working The third brake light or "center high-mounted stop lamp" is not working.
However, because of its location, problems with the third brake light (also known as center high-mount stop lamp) are often caused by other reasons. For example, in many cars and pickup trucks, water can leak inside the third brake light assembly or connector and cause corrosion. In this case, not only will the bulb(s) have to be changed, but the light assembly must be re-sealed or replaced if an old seal is too damaged. The connector must be checked for corrosion too.
Trunk lid harness Trunk lid harness.
See how a corroded connector looks.

If a third brake light or other lights are installed on a trunk lid or a liftgate, another common problem is a broken wire inside the harness that connects to the trunk lid or liftgate. In older high-mileage vehicles, repeated opening and closing of the trunk lid or liftgate can cause the wires inside the harness to break or short between each other. For example, this issue is common in older German cars. Often, shorted wires in the harness can cause the brake light fuse to blow. If the third brake light is not working, check the bulb(s) and look for signs of corrosion. If the bulbs are not burned, the problem must be diagnosed.

Both taillights or all three brake lights don't work. Although it's rare for two or three bulbs to fail at the same time, bulbs must be checked first.
Third brake light is not working One of the ways to check brake lights is to look at the reflection when you park your car near the reflective wall.
If the bulbs are good, it means that the electric circuit for the affected lights is down. For example, a bad brake light switch can cause the brake light circuit (and all three brake lights) to not work. If the electric circuit is down, the first step is to check the fuse.

Most cars have two or three fuse boxes; you can find the fuse location in the owner's manual. One circuit can have more than one fuse. If all the fuses are OK, the circuit must be diagnosed. In modern cars, lights are controlled by electronic control modules. Mechanics at a dealership or well-equipped auto repair shop can check any of the control modules with a scan tool and multimeter.

The fuse for the affected lights is blown. A blown fuse is easy to replace, but If the fuse is blown, it means there is an electrical short somewhere in the affected circuit. For example, one of the bulbs could be shorted or installed the wrong way, or wires that connect to the trailer harness could be rubbing against the metal part or damaged wires inside the trunk lid harness could be shorted between each other. It's not always easy to find the reason for a blown fuse, but a knowledgeable mechanic should be able to help. Most dealers and auto repair shops charge a flat fee ($50-$130) for initial diagnostics of an electrical problem like this.

Reference: 1. NHTSA Traffic Safety Facts 2017