* Brake light switch: This is the most common culprit. The brake light switch is a small mechanism that activates the brake lights when the brake pedal is pressed. If it's faulty, it might be sticking or sending a false signal, even when the pedal isn't engaged.
* Short circuit: A short circuit in the wiring harness leading to the brake lights can cause them to stay on. This could be due to damaged wiring, a corroded connection, or a problem within a component along the circuit.
* Faulty brake light bulbs: While less likely to cause the lights to stay *constantly* on, a faulty bulb can sometimes create a short circuit, leading to this problem. A bulb that's shorted internally can draw power even when it's not lit.
* Body control module (BCM): The BCM manages many electrical functions in the vehicle, including lighting. A faulty BCM could send incorrect signals to the brake light circuit. This is less likely, but possible.
* Towing wiring harness (if applicable): If you've ever used a towing harness, a fault within its wiring could cause a constant draw on the brake light circuit.
Troubleshooting Steps:
1. Visual Inspection: Start with a careful visual inspection of the brake light wiring harness, looking for any obvious damage, corrosion, or loose connections. Pay special attention to the area around the brake pedal and the wiring near the tail lights.
2. Check the Brake Light Switch: This is the easiest to check. See if you can manually move the brake light switch to see if it feels loose or sticky. Many tutorials online demonstrate how to test it with a multimeter (measures electrical voltage and continuity).
3. Test the Brake Light Bulbs: Check all three brake light bulbs (two on the rear, one on the center high-mounted stop lamp, or CHMSL). A simple visual inspection is a good first step to ensure they aren't physically damaged or loose. Consider replacing them with new bulbs.
4. Multimeter Check: If you're comfortable using a multimeter, you can test the voltage at the brake light switch and the wiring harness to identify a short circuit or other electrical issue.
5. Professional Diagnosis: If you can't find the problem yourself, take your Suburban to a qualified mechanic or auto electrician. They have the tools and expertise to diagnose more complex electrical problems. A scan tool can help read trouble codes from the BCM or other modules.
Leaving your brake lights on constantly will drain your battery. It's important to address this issue as soon as possible.
