* Brake Light Switch (despite seeming good): While you've checked it, the switch might be failing intermittently or have a subtle internal fault that only manifests when the brakes are applied. It's possible the switch is *making* contact but not *fully* making contact, offering insufficient current to the lights. Replacing the switch is often the cheapest and easiest solution first. A simple visual inspection might not reveal the problem.
* Wiring Issues: Worn, corroded, or broken wires between the brake light switch, the brake pedal, and the tail lights are common culprits. Check the wiring harness near the brake pedal and at the connection points to the taillights. Look for:
* Broken wires: These might be hidden within the harness. A visual inspection might not be sufficient. You might need to trace the wires.
* Corrosion: Green or white residue on connectors indicates corrosion, which can prevent proper electrical contact. Clean connectors thoroughly with a wire brush and contact cleaner.
* Loose connections: Connections at the back of the tail light assemblies or anywhere along the wiring harness might be loose. Ensure they are secure.
* Grounding Problem: A poor ground connection will prevent the circuit from completing. Inspect the ground wire(s) connected to the taillight assemblies. Make sure they are clean and properly secured.
* Body Control Module (BCM): In some vehicles, the BCM controls the brake lights. A faulty BCM could prevent the lights from functioning. This is less likely, but possible. Diagnostics would be needed to check this.
* Wiring harness damage near the rear axle: The harness can be pinched or chafed here, especially if towing has been done.
Troubleshooting Steps:
1. Thorough Brake Light Switch Inspection: Even if you've checked it, try replacing the brake light switch. This is the most likely culprit.
2. Visual Inspection of Wiring: Carefully inspect all wiring from the switch to the taillights, both at the connection points and along the wire harness for any damage.
3. Check Grounds: Clean and secure the ground connections at the taillights.
4. Test the Wiring: Use a multimeter to test continuity in the brake light circuit. This requires some electrical knowledge. You'll need to test for voltage at the switch and at the lights themselves when the brake pedal is depressed.
5. Consult a wiring diagram: A wiring diagram specific to your 2002 Chevy Suburban is essential for tracing the circuit accurately. These can often be found online.
If you're not comfortable working with car wiring and electricity, it's best to take your Suburban to a qualified mechanic. They have the tools and expertise to diagnose and repair the problem efficiently.
