* Wiring harness damage: The most common culprit. Rodents can chew wires, wires can chafe against metal parts, or they can simply corrode and break over time, especially in an older car. Check the wiring harness running from the taillights to the fuse box, and also the harness near the switch. Look for breaks, chafing, corrosion, or any evidence of rodent damage. This is often found near the rear bumper and where the harness goes into the body.
* Broken or faulty tail light switch: This switch is often located on the steering column and controls the parking lights and tail lights. It could be mechanically failing or have a broken internal connection.
* Faulty combination switch (turn signal/wiper switch): The combination switch is a common point of failure and can affect various functions including the parking lights and turn signals.
* Body control module (BCM) issues: The BCM controls many electrical functions in the car. A malfunctioning BCM could be preventing the lights from functioning, even with good fuses and switches. This is less likely, but possible.
* Ground fault: A poor ground connection can prevent the lights from working. Check the ground wires associated with the taillights and make sure they are clean and securely connected. These are typically found on the car body near the tail light assemblies.
* Faulty taillight assemblies themselves: Though less probable if *both* sides are out, it's possible that both taillight units have internal problems. This is usually a bulb issue, but it's possible the internal wiring is bad within the assembly itself.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine all wiring harnesses related to the taillights and parking lights. Look for any obvious damage.
2. Test the Bulbs: While you mentioned fuses are good, it's still worth checking the bulbs themselves. A bulb could have a broken filament even if the socket has power.
3. Check for Power at the Bulbs: Use a multimeter to test for power at the taillight sockets. You'll need to know which wires are for the park lights vs. brake lights. A wiring diagram (available online) will be very helpful. With the headlights on (parking lights), there should be power at the park light circuit.
4. Test the Switch: Test the tail light switch for continuity using a multimeter. You'll need a wiring diagram to determine the correct pins to test.
5. Check Ground Connections: Clean and tighten all ground connections related to the taillights.
If you're not comfortable working with car electrical systems, it's best to take your car to a qualified mechanic. Diagnosing electrical problems can be tricky, and a professional will have the tools and expertise to pinpoint the issue quickly and efficiently.
