* Brake light switch: This is the most common culprit. The brake light switch is a small electrical switch located near the brake pedal. If it's faulty (stuck on), it will constantly send a signal to the lights, keeping them illuminated even when the brake pedal isn't depressed.
* Wiring problem: A short circuit or a break in the wiring harness leading to the brake lights could cause them to stay on. This might be a wire rubbing against something metal, a corroded connection, or a damaged wire within the harness. This is more likely if *only* one brake light is on.
* Faulty brake light bulbs: While unlikely to cause *both* brake lights to remain constantly on, a very unusual short inside a bulb *could* theoretically do so. Replacing them is a cheap and easy first step.
* Tail light assembly issues: A short circuit within the tail light assembly itself (though less common) could also be responsible.
* Fuse problem: A blown fuse *would* prevent the brake lights from working, but a *short* in the circuit could cause a fuse to blow repeatedly, leading to lights that might flicker before going completely out, or lights that sometimes work and sometimes don't. A partial short could keep them on. This is less likely given they are *always* on.
Troubleshooting Steps:
1. Check the brake light bulbs: Replace them with new ones, even if they seem fine. This is the easiest check first.
2. Inspect the brake light switch: Locate the switch (usually near the brake pedal). Try gently pressing and releasing the switch while observing if the brake lights turn on and off. If it doesn't switch reliably, it needs replacing.
3. Check the fuses: Consult your owner's manual to locate the fuse(s) for the brake lights. Check if they're blown. If so, replace them, but be aware that a constantly blowing fuse points to a short circuit elsewhere in the system.
4. Inspect the wiring: Visually examine the wiring harness leading from the brake light switch to the tail lights. Look for any obvious damage, corrosion, or frayed wires. Pay close attention to areas where wires might rub against metal parts.
If you're not comfortable working with car electrical systems, it's best to take your car to a qualified mechanic for diagnosis and repair. Ignoring a constantly on brake light can drain your battery and cause other issues.
