* Bulbs: The most common cause is simply blown taillight bulbs. Check all the bulbs in the taillights (left and right). Make sure they're the correct wattage.
* Fuses: A blown fuse in the taillight circuit will prevent them from working. Check your vehicle's fuse box (usually under the hood or inside the cabin) for a fuse related to the taillights. Your owner's manual will show you the fuse box layout and which fuse controls the taillights.
* Wiring: A break or short in the wiring harness leading to the taillights is possible. This is more difficult to diagnose and might require tracing the wires to find the problem. Look for any frayed or damaged wires near the taillights or where the harness runs.
* Tail Light Switch: While less likely given that the brake light works (which uses a different switch), a faulty tail light switch could be the problem. This switch is activated when the lights are turned on.
* Ground Connection: A poor ground connection can prevent the taillights from working. Ensure the ground wires at the taillights are clean and making good contact.
* Body Control Module (BCM): In some vehicles, the BCM controls the lighting system. A faulty BCM is less likely but possible. This requires more advanced diagnostic tools.
Troubleshooting Steps:
1. Check the Bulbs: This is the easiest and most likely solution. Replace any burnt-out bulbs.
2. Check the Fuses: Locate and inspect the taillight fuses.
3. Visual Inspection of Wiring: Carefully examine the wiring harness for any damage.
4. Test the Ground Connection: Clean the ground connection points at the taillights.
5. Advanced Diagnostics (If Necessary): If the above steps don't solve the problem, you'll likely need a multimeter to test the voltage and continuity of the wiring and circuits, or a professional mechanic to diagnose more complex issues like the BCM.
Remember to always disconnect the negative battery terminal before working on any electrical components in your car.
