Owner's Problem Description
The owner reports that the brake lights on both the right and left tail lights are not functioning, although the brake light on the rear door is operational. They have checked all fuses under the hood and under the rear seat, and have also inspected the bulbs, which are in good condition. The owner is unsure of the next steps and is seeking assistance.
Professional Technical Analysis
The 2006 Isuzu Ascender, equipped with a conventional lighting system, exhibits a failure of the brake lights on both the left and right tail lights while the rear door light functions correctly. This symptom suggests issues within the wiring or control circuits associated with the tail light assembly. The vehicle's electrical system is interconnected, meaning that a fault in the brake light circuit can often be traced back to the switch, wiring harness, or connectors. Since the owner has already checked the fuses and bulbs, the next logical step is to investigate the brake light switch and the wiring leading to the tail light assemblies. The brake light switch, typically located near the brake pedal, can fail or become misaligned, preventing the brake lights from receiving power. Additionally, corrosion or damage in the wiring harness, especially near the trailer wiring connector, could lead to an open circuit. Testing the voltage at the tail light connectors with a multimeter can confirm whether power is reaching the lights when the brake pedal is pressed. If voltage is present but the lights do not illuminate, the issue is likely within the tail light assembly itself. Furthermore, considering the vehicle's age and potential exposure to harsh environmental conditions, wiring degradation over time is a plausible cause. Safety is paramount, and addressing this issue is crucial for proper signaling on the road.
Possible Causes
Most common causes (ordered by frequency):
- Brake Light Switch Failure: A common issue, the brake light switch may fail or misalign, preventing power from reaching the tail lights. Typically located above the brake pedal, the switch should show continuity when activated. Testing the switch with a multimeter should yield a resistance of less than 1 ohm when the pedal is pressed. If failed, replacement with OEM part 15134694 is recommended. - Lack of power at tail light connectors when brake pedal is pressed, continuity test results showing open circuit.
- Wiring Harness Issues: The wiring harness between the brake light switch and the tail light assemblies may have corrosion or damage, especially around the trailer wiring connector. This can create an open circuit condition, preventing the brake lights from illuminating. Checking for continuity and inspecting for physical damage or corrosion is essential. - Visual inspection shows signs of corrosion at the trailer connector, continuity tests reveal open circuit in the harness.
- Tail Light Assembly Failure: The tail light assemblies themselves may have internal failures, such as broken solder joints or burnt-out circuits. Testing the tail lights directly for voltage presence when activating the brake pedal can confirm whether the assemblies are functioning correctly. - Testing reveals no voltage at the tail light connectors despite power at the switch, indicating potential failure of the assembly.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Inspection: Begin with a thorough visual inspection of the tail light assemblies and wiring. Check for any visible signs of damage or corrosion at the connectors and along the wiring harness. Ensure the integrity of the brake light bulbs by testing them independently with a multimeter.
- STEP 2 - Brake Light Switch Testing: Locate the brake light switch and test for continuity using a multimeter. With the brake pedal depressed, the switch should exhibit continuity (less than 1 ohm). If no continuity is detected, replace the switch with OEM part number 15134694.
- STEP 3 - Wiring Continuity Check: Inspect the wiring harness connecting the brake light switch to the tail lights, especially at the trailer wiring connector. Use a multimeter to test for continuity throughout the circuit. Repair any damaged wires or connections identified during this inspection.
- STEP 4 - Tail Light Assembly Testing: If previous steps show no faults, test the tail light assemblies by measuring voltage at the connectors when the brake pedal is pressed. If voltage is present but the lights do not illuminate, the assemblies may require replacement.
