How do I know which bulb is the brake light?

In most vehicles, the brake light is either a dedicated bulb in the tail-light cluster or a dual‑filament bulb that has a separate brake filament. In newer cars, LED brake lighting may be a module rather than a replaceable bulb.

Brake light configurations you may encounter

Different vehicles use different tail-light arrangements. Knowing the common setups helps you identify the correct component at a glance.

• Dual-filament bulbs in a single socket: one filament powers the taillight (running light) and the other lights when you brake, producing a brighter brake signal.


• Two separate bulbs in the same housing: one bulb is dedicated to the brake signal, the other to the taillight/parking light.


• LED tail-light modules: the brake signal comes from an LED cluster or module rather than a traditional bulb; replacement usually means swapping the module or entire tail-light unit.

Conclusion: Most cars fall into one of these categories, though exact base types and locations vary by model. If you’re unsure, check your owner’s manual or a repair guide for your exact vehicle.

Step-by-step: identify the brake light bulb on your vehicle

Use these steps to locate and confirm which bulb performs braking in your tail-light assembly. The exact method can differ by make and year, but the approach is broadly the same.

1. Open the trunk or tailgate and locate the tail-light assembly on the side you are inspecting.


2. Remove the access panel or tail-light cover as described in your owner's manual, which may require removing a screw or prying out a cover.


3. Observe how many bulbs are in the housing: a single dual-filament bulb or two separate bulbs.


4. If it’s a dual-filament bulb, identify which filament brightens when you press the brake; that filament is the brake light.


5. Note the bulb base or part number for replacement; common dual-filament bases include families like 1157/1157A, but many vehicles use different bases. Use the bulb you remove as a reference or check a parts store for the exact base.


6. Test by having a helper press the brake pedal while you observe to confirm which bulb or filament lights up.

Conclusion: After identifying the brake light bulb, you can proceed to replace it with the correct part and reassemble the tail-light assembly.

Special case: LED tail lights

Some newer vehicles use LED brake lighting that is not a replaceable bulb. In those cases, the brake signal is provided by an LED module or cluster, and replacement often means swapping the module or the entire tail-light unit rather than a single bulb. Refer to your owner's manual or a dealership/repair guide for exact guidance.

Testing, safety, and care

Once you’ve replaced a bulb or module, confirm operation by pressing the brake pedal as appropriate for your vehicle. Also verify that the taillight and turn signals function correctly. When handling bulbs, avoid touching the glass with bare fingers; oils can shorten bulb life. Reinstall covers and secure all fasteners after testing.

If you’re unsure or uncomfortable performing the replacement, seek professional assistance. Properly functioning brake lights are essential for road safety and legal compliance.

Summary

Brake-light identification depends on your vehicle’s design: a dual-filament bulb, two separate bulbs in the tail-light housing, or an LED brake-light module. Use the owner’s manual to locate the exact component, inspect the assembly to determine which part provides braking, and replace with the correct part. After replacement, test thoroughly to ensure a bright and reliable brake signal.

Which one is a brake light?

The brake light is the red, brighter light on the back of your vehicle that turns on only when you press the brake pedal. It is located near or within the same housing as the taillight, which is a dimmer red light that is on whenever the headlights or parking lights are on. Many vehicles have two outer brake lights and a third, center high-mount stop lamp.
 
This video explains the difference between tail lights and brake lights: 55sKamsiparts Automotive YouTube · Feb 17, 2024
How to tell the difference

• Activation: The brake light is activated only when you press the brake pedal. The taillight is on whenever the headlights or parking lights are on. 
• Brightness: The brake light is significantly brighter than the taillight to signal that you are slowing down. 
• Location: Look for the lights on the rear of your car. 
  • You will have two outer brake lights, which are often integrated with the taillights. 
  • Many modern cars also have a third, center brake light, which may be mounted higher up in the rear window or on the trunk. 

If your brake lights aren't working

• Check the bulb: Many cars use a dual-filament bulb, where the dimmer filament is for the taillight and the brighter one is for the brake light. If only one is working, the bulb needs to be replaced. 
• Check the fuse or switch: If both brake lights are out, it could be a blown fuse or a problem with the brake light switch. 

Which bulb is the brake light?

On many vehicles, the tail lights and brake lights share the same bulb. One filament inside the bulb is for the tail light and the other filament is for the brake light. There are also some vehicles that have a separate bulb for each circuit.

How do I know which brake light bulb I need?

To find the right brake light bulb, you can check your vehicle's manual, look for the number printed on the old bulb, or use an online fit guide from a parts store. Common bulb types include 1157, 3157, and 7443, but it is essential to get the correct one for your specific car.
 
You can watch this video to learn how to find the correct bulb size for your car: 50sHomeowner RepairYouTube · Jul 14, 2018
Methods to find the correct bulb

• Vehicle manual: Your car's owner's manual will specify the exact bulb type needed for a guaranteed fit. 
• Existing bulb: Remove the old bulb and look for a number printed on it (e.g., 1157, 3157). 
• Online tools: Many auto parts retailers, such as AutoZone and Walmart, have online tools where you can enter your car's year, make, and model to find the compatible bulb. 
• Go to a store: Visit a local auto parts store and ask for assistance. They can look up the correct bulb for you or help you read the number off your old bulb. 

Other considerations

• Dual-function bulbs: Many brake lights use a dual-filament bulb that serves as both a tail light and a brake light (e.g., 1157, 3157). 
• LED vs. Incandescent: You can replace your old bulbs with LED versions, which are often brighter and longer-lasting. However, some vehicles may trigger a dashboard warning light when an LED bulb is installed. 

You can watch this video to learn about the difference between LED and incandescent bulbs: 1mspeedkar99YouTube · Nov 9, 2015

How do I tell which light bulb I have?

To identify a light bulb, start by checking the bulb itself for printed information like wattage, type (LED, incandescent, etc.), and color temperature. If you can't find that, look at the bulb's shape and size, as these are often indicated by a letter and number code (like "A19") where the letter denotes the shape and the number is the diameter in eighths of an inch. Finally, examine the base to determine its type (e.g., screw-in or pin) and size, which is often a letter-number combination like "E26" for a standard screw-in or "GU24" for a two-pin base.
 
This video explains how to identify a light bulb's shape and size: 53sAMRE SupplyYouTube · Jul 5, 2020
What to look for

• Information printed on the bulb: The easiest way is to look for the manufacturer's markings directly on the glass or metal base. You may find details like:
  • Wattage: The power consumption (e.g., 606060W).
  • Type: The technology used to produce light (e.g., LED, incandescent, halogen).
  • Voltage: The required voltage (e.g., 120120120V).
  • Shape/Size Code: A letter-number code that specifies the shape and diameter.
  • Color Temperature: Measured in Kelvin (K), which indicates the color of the light (e.g., 270027002700K for warm white). 

You can watch this video to learn how to choose the right light bulb: 42sLowe's Home ImprovementYouTube · Jan 4, 2023
How to interpret codes

• Shape and size code: Codes like "A19" or "PAR30" are common. 
  • The first letter(s) indicate the shape (e.g., 'A' for standard household, 'PAR' for parabolic aluminized reflector). 
  • The number is the diameter in eighths of an inch. For example, a "19" means 19/819 / 819/8 of an inch, or about 2.3752.3752.375 inches. 
• Base code: Codes like "E26" or "GU24" describe the base that connects to the socket. 
  • The letter(s) indicate the base type (e.g., 'E' for Edison screw, 'GU' for a specific pin base). 
  • The number is the diameter or the distance between pins. For an "E26," the '26' means the diameter is 26 millimeters, which is the standard household screw-in base. A "GU24" has two pins spaced 24 millimeters apart. 

This video shows how to test a light bulb with a multimeter: 56sElectro UniversityYouTube · Dec 27, 2023
If the bulb has no markings 

• Take the old bulb with you: The easiest method is to take the old bulb to the store to find a match for its base and shape. 
• Identify the base type: If it's a screw-in base, measure its diameter in millimeters. For other types like pin-based bulbs, count the number of pins and measure the distance between them. 
• Measure the diameter: If the base is a standard screw-in type, you can also measure the bulb's widest part in eighths of an inch. 
• Look for physical clues: 
  • Incandescent: Often has a visible filament inside. 
  • CFL: Looks like a bent or spiral tube, and you might see yellowing chips inside. 
  • LED: Often has a plastic base and a plastic cover, and some may have small, what appear to be "chips" inside while the bulb is off.