1. Brake Light Switch: This is the most common cause. The brake light switch is a small switch located near the brake pedal. It's activated when you press the brake pedal, completing the circuit to turn on the brake lights.
* Troubleshooting:
* Visual Inspection: Check the brake light switch for any obvious damage or loose connections. It might be cracked or corroded.
* Continuity Test: You'll need a multimeter. Disconnect the switch and test for continuity (electrical connection) when the brake pedal is pressed and released. There should be continuity only when the pedal is pressed. If there's no change in continuity, the switch is faulty.
* Replacement: If faulty, replacing the brake light switch is relatively inexpensive and straightforward. You can find replacement switches at auto parts stores. Be sure to get one specifically for your 1993 Nissan Sentra.
2. Brake Light Bulbs: While you say the taillights work, it's possible one or both brake light bulbs are burned out. The taillights might use different bulbs (separate filaments) than the brake lights.
* Troubleshooting: Inspect the brake light bulbs themselves. Replace them if burned out or damaged.
3. Wiring Issues: A break or short in the wiring between the brake light switch and the taillights could be the problem.
* Troubleshooting: This requires more advanced troubleshooting. You'll need a wiring diagram for your specific car model to trace the wires. A multimeter can be used to check for continuity and voltage at various points along the wiring. Look for any damaged or corroded wires, particularly near the brake pedal and taillight assemblies.
4. Fuse: Though less likely if the taillights work, a blown fuse in the brake light circuit is possible.
* Troubleshooting: Check your owner's manual for the fuse box location and diagram. Locate the fuse related to the brake lights and check if it's blown (usually indicated by a broken filament). Replace it with a fuse of the same amperage if necessary.
5. Grounding Issues: A poor ground connection at the taillight assembly could interrupt the brake light circuit.
* Troubleshooting: Inspect the ground wires at the taillights for corrosion or loose connections. Clean any corrosion and ensure tight connections.
Troubleshooting Steps (Recommended Order):
1. Check the Brake Light Switch: This is the most likely culprit.
2. Check the Brake Light Bulbs: Easy and quick check.
3. Check the Fuse: A simple check.
4. Inspect Wiring: This is more complex and requires more knowledge and tools.
5. Check Grounding: Another area that can easily be overlooked.
If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and safely.
