* Brake Light Switch: This switch is a normally-closed (NC) type. When the brake pedal is *not* pressed, the switch completes the circuit, allowing the brake lights to remain OFF. When you press the brake pedal, the switch opens, breaking the circuit and turning the brake lights ON. If the switch is malfunctioning and stuck in the "open" position (or has a faulty internal contact), the lights will stay on all the time. Pressing the brake pedal then further disrupts the already broken circuit, turning the lights off.
* Wiring Issues: A short circuit in the wiring leading to the brake light switch could also cause this. A short to ground after the switch (but before the lights) would keep the lights on. Pressing the brake pedal might interrupt this short, turning the lights off.
Troubleshooting Steps:
1. Inspect the Brake Light Switch: This is the most likely culprit. Locate the brake light switch (usually on the brake pedal assembly). It's a small cylindrical switch. Visually inspect it for any obvious damage. If possible, try gently moving it to see if it feels loose or sticky.
2. Check the Wiring: Carefully examine the wiring connected to the brake light switch for any signs of damage, chafing, or corrosion. Look for broken insulation or wires that might be touching each other or the chassis.
3. Test the Switch (if possible): If you have a multimeter, you can test the switch's continuity. With the brake pedal not pressed, the switch should be closed (continuity). When pressed, it should be open (no continuity). If it doesn't follow this pattern, replace it.
4. Test the Bulbs: While less likely given the description, make sure all your brake light bulbs are functioning correctly. A faulty bulb can sometimes cause strange electrical issues in the system.
Important Safety Note: Don't work on your brake system unless you are familiar with automotive repair. If you're unsure, take your truck to a qualified mechanic to have it diagnosed and repaired. Driving with malfunctioning brake lights is dangerous.
