Possible Causes:
* Burnt-out Brake Light Bulbs: This is the most common and easiest fix. Check all three brake light bulbs (one in the center high-mounted stop lamp (CHMSL) and one in each taillight). Replace any that are burnt out.
* Blown Fuse: Check the fuse box (usually under the hood or inside the vehicle) for a blown fuse related to the brake lights. Your owner's manual will show you the fuse diagram. Look for fuses labeled "brake," "stop," or something similar.
* Faulty Brake Light Switch: This switch, located on the brake pedal, activates the brake lights when the pedal is depressed. A faulty switch will prevent the brake lights from working. This is a common failure point.
* Wiring Issues: A broken or corroded wire in the brake light circuit can interrupt the signal. This might be anywhere from the brake light switch to the bulbs themselves. Inspect the wiring harness for damage, especially near the taillights and brake pedal.
* Faulty Tail Light Assemblies: While less likely if your running lights and turn signals work, a problem within the taillight assembly itself could affect the brake light circuit.
* Central Tail Light Control Module (less likely): Some vehicles have a control module that manages the taillights. While less common on a 1999 Suburban, a malfunctioning module is a possibility.
Troubleshooting Steps:
1. Check the Bulbs: This is the first and easiest step. Replace any burnt-out bulbs.
2. Check the Fuses: Consult your owner's manual to locate and check the appropriate fuses.
3. Test the Brake Light Switch: You can test this yourself by having someone press the brake pedal while you check for 12V power at the brake light switch wires. (Use a multimeter. Caution: Be careful working with electricity. If you are uncomfortable doing this, take it to a mechanic.)
4. Inspect the Wiring: Carefully examine the wiring harness from the brake light switch to the taillights. Look for any broken, frayed, or corroded wires.
5. Check for Power at the Taillight Connectors: With the brake pedal depressed, use a multimeter to check for 12V power at the taillight connectors. This will help isolate whether the problem is before or after the taillights.
If you're not comfortable working with car electrical systems, take your Suburban to a qualified mechanic. They have the tools and expertise to diagnose and repair the problem safely and efficiently. Trying to troubleshoot electrical problems without proper knowledge can be dangerous.
