Owner's Problem Description
The owner of a 1988 Volvo 240 reports that the brake lights are not functioning despite cleaning the sockets, changing the bulbs, and checking the brake light switch. The brake lights remain inoperative, and recently, both the failure brake lights and battery warning lights illuminated on the dashboard, indicating a potential electrical issue.
Professional Technical Analysis
This 1988 Volvo 240 is exhibiting a failure of the brake lights despite preliminary checks and part replacements. The vehicle has likely accumulated significant mileage, possibly exceeding 200,000 miles, which can contribute to electrical failures, particularly in older vehicles. The symptoms indicate an electrical issue, likely involving the brake light switch or associated wiring. The fact that both the brake light failure and battery warning lights have illuminated suggests a potential problem with the vehicle's electrical system, possibly indicating voltage irregularities or ground issues. The brake light switch, located on the brake pedal assembly, requires power to operate the brake lights. It is crucial to verify that the switch is receiving a stable voltage of around 12V, as well as checking the integrity of the ground connection. Additionally, inspect the wiring harness for any signs of wear or corrosion, which could lead to intermittent failures. Given the age of the vehicle, it's also advisable to check the fuse box for any signs of corrosion or damage, and ensure all related fuses are intact. The possibility of a faulty brake light switch cannot be discounted, particularly if it is not passing voltage to the brake lights even when power is present. Perform a continuity test on the switch to confirm its operational status. In my experience, intermittent electrical issues in older Volvos often stem from corroded connections or worn-out components. Ensuring all grounds are clean and connections are secure is essential in resolving this issue.
Possible Causes
Most common causes (ordered by frequency):
- Brake Light Switch Failure: The brake light switch may be faulty despite receiving power. It typically operates with a nominal input of 12V and can fail internally, leading to no output to the brake lights. Testing for continuity across the switch when engaged is essential to confirm functionality. Replacement part, OEM P/N 1341957, is recommended if failure is confirmed. Symptoms include brake lights remaining off even with power supplied. - Power present at the switch but no voltage output to lights, continuity test failure across the switch.
- Corroded or Damaged Wiring: The wiring harness that connects the brake light switch to the brake lights may be corroded or damaged. This can cause an intermittent loss of connection. Visual inspection of the harness, particularly at connection points, is crucial. Voltage drop tests should be performed along the circuit to ensure proper operation. Repairing or replacing damaged wiring is essential to restore functionality. - Visible corrosion on connectors, voltage drop observed when tested across the harness.
- Blown Fuse or Poor Fuse Connection: Although the owner mentioned that all fuses are fine, it is important to inspect the fuse box for any signs of corrosion or poor connections which can cause intermittent faults. A blown fuse associated with the brake lights can interrupt the circuit. Verify each fuse with a multimeter for continuity to ensure they are functioning properly. - Fuse continuity test showing one or more fuses failing under load.
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 - Visual Inspection: Begin with a thorough visual inspection of the brake light switch and wiring harness. Look for any signs of fraying, corrosion, or disconnections that could lead to failure. Ensure all connections are secure and free from corrosion. This step often reveals visible issues that need immediate attention.
- STEP 2 - Brake Light Switch Testing: Perform a continuity test on the brake light switch. With the switch engaged, use a multimeter to check for continuity. It should read near zero ohms if functioning correctly. If there is no continuity or resistance is high (greater than 5 ohms), replace the switch with OEM P/N 1341957.
- STEP 3 - Wiring and Fuse Testing: Check all relevant fuses in the fuse box for continuity using a multimeter. Inspect the wiring from the brake light switch to the brake lights for voltage drop while the brake pedal is pressed. Ensure voltage remains stable at 12V. If fluctuations are detected, repair or replace the wiring as needed.
- STEP 4 - Functionality Verification: After any repairs, reconnect all components and conduct a functionality test of the brake lights. Ensure all connections are secure and check for proper operation. Use the GeekOBD APP to monitor any related fault codes that may appear during operation.
