Possible Causes:
* Brake light switch: This is the most common culprit. The switch, located near the brake pedal, might be faulty and sending a constant signal even when the pedal isn't depressed. It could be sticking, internally shorted, or simply worn out.
* Wiring issue: A short circuit or damaged wire in the brake light wiring harness leading to the cab lights is possible. This could be a break in the wire, a frayed wire touching ground, or a connection problem at a splice. Since the bed lights work, the problem is likely isolated to the cab wiring.
* Brake light circuit board (if equipped): Some vehicles have a circuit board that controls the brake lights. A problem with this board could cause the issue. This is less likely but possible.
* Faulty brake light bulb (less likely): While less probable given the bed lights work, a faulty bulb in the cab (if it has separate bulbs for brake lights and tail lights) could cause a short circuit that keeps the brake light on.
Troubleshooting Steps:
1. Check the Brake Light Switch: This is the easiest and most likely solution. You'll likely need to access it from under the dash. Visually inspect it for damage. Try gently wiggling the switch while someone observes the brake lights. If the lights flicker or turn off, the switch is likely bad.
2. Inspect the Wiring: Carefully inspect the wiring harness from the brake light switch to the cab brake light(s). Look for any visible damage, frayed wires, or loose connections. Pay close attention to any areas where the wiring might be pinched or chafed.
3. Test the Bulbs (Cab and Bed): Although you said the bed lights work, check the bulbs in the cab to ensure they aren't causing a short. If the cab lights have separate bulbs for brake and tail, check them individually.
4. Use a multimeter (advanced): If you're comfortable with electrical testing, a multimeter can help you trace the circuit. You can check the voltage at the brake light switch and at the cab lights to pinpoint where the short might be.
Important Note: If you are not comfortable working with automotive electrical systems, it's best to take your Silverado to a qualified mechanic. Incorrect wiring can lead to further damage or even a fire.
Remember to always disconnect the battery's negative terminal before working on any electrical components in your vehicle for safety.
