* Bad Ground: The most common reason is a poor ground connection for the tail light circuit. Corrosion or a loose connection in the wiring harness leading to the tail light assembly can cause the bulb to not register as "good" even if the bulb is working. Inspect the ground wire(s) at the tail light assembly for corrosion and ensure they are securely attached.
* Faulty Bulb: While you've replaced the bulb, it's possible the new bulb is defective. Try a known good bulb.
* Wiring Problem: A break or short in the wiring between the light and the instrument panel can trick the system into thinking the bulb is out. This is more difficult to diagnose and may require tracing the wiring.
* Faulty Instrument Cluster: Though less likely, the instrument cluster itself could be faulty and incorrectly reporting the bulb status. This is harder to fix and would likely require professional attention.
* Bad Tail Light Socket: The socket itself might be damaged or corroded, preventing proper contact with the new bulb. Inspect it carefully.
Troubleshooting Steps:
1. Check the new bulb again: Make absolutely sure the new bulb is correctly seated and functioning in its socket.
2. Inspect the wiring and ground: Look for any signs of corrosion, breakage, or loose connections in the wiring harness at both the tail light and the instrument panel's related connector. Pay close attention to the ground wires. Clean any corrosion found.
3. Test the bulb with a multimeter: If you have a multimeter, check the voltage at the bulb socket to confirm power is reaching the bulb. You should have power when the tail lights are switched on.
4. Check the other tail light: See if the other tail light works as expected. If both have issues, a wiring or ground problem is more likely than individual bulb faults.
5. Check the fuses: While less likely to cause just *one* tail light to register as burnt, a blown fuse related to the tail lights could also be the culprit. Check your owner's manual to find the location and rating of the relevant fuse(s).
If you've checked all of these and the problem persists, it's best to consult a qualified mechanic. They have the tools and expertise to diagnose the issue accurately.
