The brake light system is a simple on and off exterior lighting system which is controlled by a brake light switch located near the top of the brake pedal. A simple wiring circuit is connected to the car’s BCM and then onto the rear brake lamps (older cars do not use a BCM – body control module). This system is powered and protected by a fuse located inside the fuse panel under the dash or the power distribution center located under the hood.
When the brake pedal is depressed by the driver the brake light switch completes an electrical circuit. This is achieved by the switch plunger resting against the pedal arm. A stop light switch is designed in the opposite way of a normal switch because when the switch has contact by the pedal it is off, and when pedal is depressed the switch is on. This switch uses a ground trigger for BCM which will turn on the power for the three brake lights. On older vehicles the switch connects power to the brake lights directly. Some German build cars use a lighting control module in place of a BCM. A brake lamp switch is designed to work with at least two wires and up to six wires in the switch harness. These additional wires are on older cars which send signals to various additional controls in the vehicle such as the cruise control, ABS, traction control, shift lock control and BCM inputs.
American made vehicles incorporate the car’s blinkers into the brake light circuit. When the turn signal switch or multi function switch is operated the brake light circuit is substituted for the turn signal circuit for either right or left directionals. European and Japanese cars have a separate light and circuit for the brake and turn signal lights.
The most simple of all brake light problems is the fact that the bulbs simply burn out. This is an quick and easy fix in most cases. We will show you how to replace these bulbs further on in this guide. As in any electrical system an open or short circuit can occur interrupting the operation of one or all of the brake lamps. Lack of power to the brake lights can include:
Burned out brake light bulb
Blown brake light fuse
Broken wire in the harness
Poor connection at the bulb socket
Body control module (BCM) shorted
Brake light switch not working
Turn signal or multi function switch failure
Through time and usage the contacts inside the brake light switch can become worn and burn out rendering the switch non operational. A bad ground in the system can cause the electrical current to back feed which makes the bulb dim or dull. A poor connection at the bulb will make it flicker.
How Much Does It Cost?
If you are having the bulb replaced at a repair shop the cost can be quite reasonable, between $35.00 and $55.00 (US). If you are going to replace the bulb yourself and save the trip to the garage which is what most people do the bulb will cost between $5.00 and $8.00 (US) dollars on Amazon or at the local auto parts store. If the bulbs are okay and you have an electrical problem the costs can go up considerably which can range from $150.00 to $300.00 (US) for labor alone. We will show you how to find these kinds of problems further down in this repair guide.
How Long Do Brake Lamps Last?
Brake light bulbs should last up to 40,000 miles or 4 years depending on driving conditions such as stop and go traffic. When replacing lighting bulbs use high quality replacement parts to ensure proper operation and a longer lifespan of the repair. Cheaply made bulbs tend to burn out more rapidly which requires a repeat replacement. The electrical portion of the system should be trouble free for at least 100,000 miles or 8 years.