* Wiring issue: This is the most probable cause. A broken, corroded, or loose wire somewhere in the circuit leading to those lights is preventing power from reaching them. The wiring harness runs through areas prone to wear and tear, especially near the rear hatch or tailgate. Check the wiring carefully for any damage, especially near the connections at the lights themselves and where the harness enters the body.
* Faulty switch or relay: Although less likely if the fuses are intact, a faulty brake light switch or a relay in the electrical system could be the culprit. The brake light switch is usually located near the brake pedal, and a faulty relay can prevent the circuit from completing. A multimeter can help test these components.
* Ground connection problem: A poor ground connection can prevent the lights from working. Ensure the grounds for both the license plate light and CHMSL are clean and making good contact with the car's body.
* Multi-function switch (rare): In some rare instances, a failing multi-function switch (the stalk that controls your turn signals, wipers, etc.) can cause issues with the brake lights.
Troubleshooting steps:
1. Visually inspect wiring: Carefully examine the wiring harness leading to the license plate light and the CHMSL. Look for any breaks, chafing, corrosion, or loose connections. Pay close attention to the areas where the wiring passes through the body and near the lights themselves.
2. Test the bulbs (again): Even if you think they're good, try swapping the bulbs with known good ones from another light fixture on the car (e.g., a front turn signal). This eliminates any doubt about the bulbs.
3. Check the ground connection: Locate the ground wires for both lights. Clean them with a wire brush and reconnect them securely.
4. Test the circuit with a multimeter: If you're comfortable with electrical testing, use a multimeter to check for voltage at the lights' sockets. You should have voltage when the brakes are applied (for the CHMSL and license plate light), and also voltage at the license plate light when the lights are turned on. A lack of voltage at the socket indicates a wiring or switch problem.
5. Check the brake light switch: This might require accessing the switch near the brake pedal, which may involve removing some trim pieces. A malfunctioning switch may not be supplying power when the brake is pressed.
6. Seek professional help: If you're not comfortable with electrical work, take your car to a qualified mechanic. They have the tools and expertise to diagnose and repair the problem efficiently.
Remember safety first. Disconnect the negative battery terminal before doing any electrical work.
