The brake light relay is a crucial component in your vehicle's electrical system. It ensures that your brake lights illuminate properly when you press the brake pedal, alerting other drivers to your intention to slow down or stop. Knowing its location can be vital for troubleshooting and resolving issues that might compromise your safety on the road. This guide will provide you with the necessary information to locate the brake light relay in various vehicles and understand its function.
| Vehicle Type/System | Typical Relay Location | Notes |
|---|---|---|
| General/Most Vehicles | Fuse Box (Engine Compartment or Under Dash) | Consult your vehicle's owner's manual for the specific fuse box diagram. |
| Older Vehicles (Pre-1990s) | Firewall or Under the Dashboard | May be less standardized; requires careful visual inspection. |
| Ford Trucks/SUVs | Central Junction Box (CJB) under the dash | Often located behind the glove compartment or to the left of the steering column. |
| GM Trucks/SUVs | Underhood Fuse Box | Check the cover for a diagram indicating the brake light relay. |
| Chrysler/Dodge/Jeep | Power Distribution Center (PDC) in Engine Compartment | Similar to GM, consult the PDC cover diagram. |
| European Vehicles (BMW, Mercedes, VW) | Fuse/Relay Box (Engine Compartment or Interior) | Locations can vary greatly depending on the model and year. |
| Japanese Vehicles (Toyota, Honda, Nissan) | Relay Box (Under Hood or Inside Cabin) | Look for a relay box near the fuse box with a clear cover. |
| Vehicles with Trailer Tow Package | Auxiliary Relay Box (Engine Compartment or Near Taillights) | May have a separate relay for trailer brake lights. |
| Vehicles with Integrated Trailer Brake Controller | Controller Wiring Harness (Under Dash) | Relay may be integrated into the controller wiring. |
| Vehicles with ABS (Anti-lock Braking System) | ABS Control Module (Engine Compartment) | The brake light relay may be incorporated into the ABS system. |
Detailed Explanations
General/Most Vehicles: The most common location for the brake light relay is within one of the vehicle's fuse boxes. These boxes are typically found in the engine compartment or underneath the dashboard, often on the driver's side. Consulting your vehicle's owner's manual is crucial as it will provide a detailed diagram of the fuse box, clearly identifying the brake light relay.
Older Vehicles (Pre-1990s): In older vehicles, the location of the brake light relay can be less standardized. It's frequently found mounted on the firewall (the metal partition separating the engine compartment from the passenger cabin) or tucked away under the dashboard. A thorough visual inspection is usually necessary to locate it in these vehicles. You may need to follow the wiring from the brake light switch to find the relay.
Ford Trucks/SUVs: Ford vehicles, particularly trucks and SUVs, often house the brake light relay within the Central Junction Box (CJB). The CJB is usually located under the dashboard, frequently behind the glove compartment or to the left of the steering column. Removing the glove compartment or accessing the area under the dash will be required to access the CJB and locate the relay. The CJB cover should have a diagram.
GM Trucks/SUVs: General Motors trucks and SUVs typically have the brake light relay located in the underhood fuse box. This fuse box is usually situated near the engine and contains various fuses and relays for different vehicle systems. Check the inside of the fuse box cover for a diagram that specifically identifies the brake light relay.
Chrysler/Dodge/Jeep: Chrysler, Dodge, and Jeep vehicles often place the brake light relay within the Power Distribution Center (PDC) in the engine compartment. The PDC is similar to the underhood fuse box found in GM vehicles. The PDC cover will typically have a diagram indicating the location of the brake light relay.
European Vehicles (BMW, Mercedes, VW): The location of the brake light relay in European vehicles like BMW, Mercedes, and VW can vary significantly depending on the specific model and year of manufacture. It can be found in either the fuse/relay box in the engine compartment or a similar box located inside the cabin. Consulting the vehicle's repair manual or online forums specific to your model is highly recommended to pinpoint the exact location.
Japanese Vehicles (Toyota, Honda, Nissan): Japanese vehicles, including Toyota, Honda, and Nissan, generally have the brake light relay located in a relay box, which is often positioned near the main fuse box. This relay box can be found either under the hood or inside the cabin. Look for a smaller box with a clear cover that allows you to see the relays inside. The cover usually has a diagram.
Vehicles with Trailer Tow Package: Vehicles equipped with a trailer tow package may have an auxiliary relay box that houses a separate relay specifically for the trailer brake lights. This auxiliary relay box is typically located in the engine compartment or near the taillights. Check the wiring harness associated with the trailer tow package to locate this additional relay box.
Vehicles with Integrated Trailer Brake Controller: If your vehicle has an integrated trailer brake controller, the brake light relay may be integrated into the controller wiring harness. This harness is usually located under the dash. Trace the wiring from the trailer brake controller to find any relays associated with the system. The controller itself might contain the relay internally.
Vehicles with ABS (Anti-lock Braking System): In some vehicles equipped with an Anti-lock Braking System (ABS), the brake light relay may be incorporated into the ABS control module. The ABS control module is typically located in the engine compartment. Consult the vehicle's wiring diagrams to determine if the brake light relay is integrated into the ABS system. This configuration is less common but possible.
Frequently Asked Questions
What does a brake light relay do? The brake light relay acts as a switch, using a small electrical signal from the brake light switch to activate the larger circuit that powers the brake lights. This prevents the brake light switch from handling the full current, protecting it from damage.
How do I know if my brake light relay is bad? Common symptoms of a bad brake light relay include brake lights that don't work, stay on constantly, or flicker intermittently. You might also hear a clicking sound from the relay when the brake pedal is not pressed.
Can I replace the brake light relay myself? Yes, replacing a brake light relay is generally a straightforward process that most DIYers can handle. However, it is always best to consult a professional if you are not sure. Ensure you disconnect the battery and consult your vehicle's repair manual for guidance.
How much does a new brake light relay cost? The cost of a new brake light relay typically ranges from $10 to $30, depending on the vehicle make and model, as well as the brand of the relay.
Where can I buy a replacement brake light relay? You can purchase a replacement brake light relay from most auto parts stores, both online and in physical locations, as well as from your local car dealership.
Conclusion
Finding the brake light relay is essential for diagnosing and fixing brake light issues. By using this guide, you can confidently locate the relay in your vehicle and take the necessary steps to ensure your brake lights function correctly, contributing to safer driving. Always consult your vehicle's owner's manual and, if needed, seek assistance from a qualified mechanic.