Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsLighting Systems Diagnosis and RepairMedium
A client reports that their vehicle's brake lights are constantly illuminated, even when the brake pedal is not pressed. The turn signals and hazard lights work correctly. Which component is the most likely cause?
- AA corroded ground wire for the brake lights
- BA faulty brake light switch
- CAn incorrect bulb installed in the tail light assembly
- DA short to power in the brake light wiring
Show answer & explanationAnswer & explanation
Correct answer: B. A faulty brake light switch
The brake light switch is designed to close the circuit and activate the brake lights when the pedal is pressed. If the brake lights are constantly on, it indicates that the switch is stuck in the closed (ON) position, or its adjustment is incorrect, keeping the circuit completed.
Why the other options are wrong
- A. A corroded ground wire would typically cause dim lights or no lights at all, not constantly illuminated lights.
- C. An incorrect bulb might cause issues like backfeeding or improper brightness, but it wouldn't typically cause the brake lights to be constantly on unless it was bridging contacts, which is highly unusual.
- D. A short to power would keep the lights on, but it's less common than a faulty switch and often leads to blown fuses or other issues.
Brake Light Switch Function
An electrical switch activated by brake pedal movement, completing the circuit to illuminate brake lights.
- Normally open, closes when pedal pressed.
- Located near the brake pedal.
- Failure can cause lights to be stuck on or off.
Memory trick: Stuck pedal, switch metal!