Common Causes:
* Brake Light Switch: This is the most frequent culprit. The switch is located near the brake pedal and tells the vehicle when the brakes are applied. If it's faulty, it might be sending a signal even when the brake isn't pressed. This switch can fail in the "on" position.
* Burnt-out Bulb (Less Likely if ALL brake lights are on): While less likely if *all* your brake lights are illuminated, a burnt-out bulb in a different circuit (like a turn signal) sometimes causes the brake lights to stay on due to a short or faulty wiring in the system. If only one brake light is on, this is more likely.
* Short Circuit in the Wiring: Worn or damaged wiring in the brake light circuit can cause a short, keeping the lights constantly on. This is often due to chafing against metal parts or damage from water intrusion.
* Faulty Brake Pedal Position Sensor (If equipped): Some models may have a sensor that detects the position of the brake pedal. A faulty sensor could send an incorrect signal. Less common on older trucks like the '93 S10.
Less Common Causes:
* Faulty Brake Light Fuse (Unlikely if all lights are on): A short might blow the fuse, but if the light is *always* on, the fuse is likely fine and the short is elsewhere.
* Faulty Tail Light Assembly: Internal short within the tail light assembly itself.
Troubleshooting Steps:
1. Check the Brake Light Switch: This is the easiest to check. Locate the switch (usually near the brake pedal), and see if it's sticking or feels loose. You might be able to gently push it in and out to see if it makes a difference. Replacing this is usually inexpensive and fairly straightforward.
2. Inspect the Bulbs: Check all brake light bulbs (both sides and the center high-mounted stop lamp, if equipped). Replace any that are burnt out.
3. Visually Inspect Wiring: Carefully examine the wiring harness leading to the brake lights for any signs of damage, fraying, or corrosion. Look for areas where wires might be rubbing against metal.
4. Test the Bulbs (If only one side is affected): If only one side's brake light is on, test that bulb in the other side's socket. If it's still on, the bulb is fine, and the problem is in the wiring or switch.
5. Check the Fuse (Last resort): If you suspect a fuse issue, check the fuse box for any blown fuses related to the brake lights. But, as mentioned before, this is less likely if all brake lights are constantly illuminated.
If you are not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic. Improperly diagnosing and repairing electrical issues can lead to further damage or safety hazards.
