Owner's Problem Description
The owner reports that the turn signals and brake lights on their 1984 BMW 318 are not functioning. They have checked all fuses and confirmed they are good. The owner also tested the signal flasher relay, which clicks when the hazard lights are activated, indicating it is operational. Despite these checks, the turn signals remain inoperative. The owner is seeking further assistance in diagnosing the issue.
Professional Technical Analysis
This 1984 BMW 318 is experiencing a failure of both the turn signal and brake light systems, which are interconnected through the multi-function switch. Given that the owner has already confirmed the integrity of fuses and the operation of the flasher relay, the next likely culprit is the multi-function switch itself. This switch is typically located on the steering column and is responsible for controlling various electrical functions including turn signals and brake lights. In this model, failure of the multi-function switch can prevent power from reaching the turn signal circuit, effectively disabling the signals. It's also crucial to consider that the brake light circuit runs through this switch, meaning that issues here could render the brake lights inoperative as well. The current vehicle condition suggests that while the owner has performed preliminary diagnostics, the multi-function switch should be tested for continuity and proper function. Voltage checks at the switch terminals (approximately 12V when activated) can help confirm its operational status. Additionally, the brake light switch may also contribute to this issue if it is faulty, as it is another potential failure point in the circuit. Overall, the vehicle’s electrical system integrity must be maintained, and all connections, especially at the multi-function switch and brake light switch, should be inspected for corrosion or wear.
Possible Causes
Most common causes (ordered by frequency):
- Multi-Function Switch Failure: The multi-function switch is responsible for controlling both the turn signals and brake lights. In this vehicle, a common failure mode is internal contact wear due to age and repeated use, which can prevent the circuit from completing. Testing should include measuring resistance across the switch terminals when activated; expected values should be near 0 ohms. If resistance is significantly higher, the switch likely requires replacement. Replacement part number is OEM P/N 61311377601, with an estimated cost of $100-150. - No turn signals or brake lights operational, resistance test on switch terminals shows high resistance, suggesting internal failure.
- Brake Light Switch Failure: The brake light switch, often located near the brake pedal, can fail due to internal wear or misalignment. If the switch does not close when the brake pedal is pressed, the brake lights will not illuminate. Testing involves checking for continuity across the switch when the pedal is depressed; continuity should be present. Replacement part number is OEM P/N 61311357601, with an estimated cost of $30-50. - Brake lights do not illuminate when pedal is pressed, continuity test on switch shows no continuity, indicating a fault.
- Flasher Relay Circuit Issue: Although the flasher relay operates as indicated by its clicking sound, issues with the circuit leading to the turn signal could prevent it from functioning. Potential causes include corroded connections or damaged wiring. A thorough inspection of the relay circuit and connections should be performed. Voltage should be checked at the relay terminals when the turn signal is activated, aiming for approximately 12V. If voltage is absent, further diagnosis of wiring integrity is needed. - Relay clicks indicating operation, but turn signals still non-functional; voltage test on relay terminals shows no voltage presence.
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 Visual Inspection: Begin with a thorough visual inspection of the turn signal and brake light systems. Check all accessible wiring for signs of damage, corrosion, or loose connections, especially at the multi-function switch and brake light switch locations. Ensure that all fuses are intact and functioning. Document any visible issues for further analysis.
- STEP 2 - Test Multi-Function Switch: Utilize a multimeter to test the multi-function switch for continuity. Disconnect the switch connector and measure resistance across the terminals when the switch is activated. Expect readings near 0 ohms; if readings are significantly higher, the switch is likely faulty and should be replaced. Use OEM P/N 61311377601 for replacement.
- STEP 3 - Brake Light Switch Testing: Check the brake light switch for continuity by measuring across its terminals while pressing the brake pedal. Continuity should be confirmed; if absent, replace the switch with OEM P/N 61311357601. Ensure proper alignment of the switch to guarantee reliable operation.
- STEP 4 - Relay Circuit Verification: Even with the flasher relay clicking, verify the voltage at the relay terminals while the turn signal is activated. Use a multimeter to check for approximately 12V; if absent, further inspect the wiring and connections leading to the relay. Document findings to determine if further action is needed.
