1. Bulbs: This is the most common cause. Check all three brake light bulbs (one in the center and one in each taillight). They may have burned out. Replace them with the correct wattage bulbs.
2. Fuses: Check the fuse(s) associated with the brake lights. Your owner's manual will show you the fuse box location and diagram. Look for blown fuses (a broken filament inside). Replace any blown fuses with the correct amperage. *Note:* A consistently blowing fuse points to a short circuit elsewhere in the system – don't just keep replacing it.
3. Brake Light Switch: This switch, located near the brake pedal, activates the brake lights when the brake pedal is pressed. It's a common failure point. It might be worn, broken, or simply out of adjustment. You can test it with a multimeter or by visually inspecting it for damage.
4. Wiring: Check the wiring from the brake light switch to the taillights. Look for broken wires, corroded connections, or loose terminals. Pay particular attention to areas where the wiring harness might rub against metal parts.
5. Brake Pedal Position Switch: Similar to the brake light switch above, this switch might be malfunctioning. Some vehicles have this in addition to, or instead of, a brake light switch.
6. Tail Light Circuitry: Issues within the taillights themselves could affect the brake lights. A short circuit within a taillight assembly can prevent all its functions (including the brake lights) from working.
7. Grounding Issues: Poor ground connections can prevent the current from flowing properly to the lights. Check the ground wires connected to the taillight assemblies and chassis.
Troubleshooting Steps:
1. Start with the simplest: Check the bulbs first.
2. Check the fuses: Replace any blown fuses.
3. Test the brake light switch: A multimeter can help determine if it's working correctly. If you're not comfortable with this, a mechanic can easily do this.
4. Inspect the wiring: Look for any visible damage or loose connections.
5. Check the ground wires: Ensure they are clean and securely connected.
If you've checked all of these and your brake lights still aren't working, you might need to consult a qualified mechanic or automotive electrician. They have the tools and expertise to diagnose more complex electrical problems. Don't drive your car with malfunctioning brake lights as it's a safety hazard.
