Why they might be related (indirectly):
* Fuse: A blown fuse could affect both systems. Check your owner's manual for the fuse locations and ratings for the brake lights and cruise control. A single fuse could power both circuits, or related circuits.
* Brake Light Switch: This switch is crucial. It signals when the brake pedal is pressed, activating the brake lights. A faulty switch might also interrupt the cruise control's operation because the system needs to know the brakes aren't engaged to maintain speed.
Why they might be unrelated:
* Separate Issues: Brake lights could be due to a bulb issue, wiring problem, or even a faulty brake light switch. Cruise control problems can stem from a variety of issues, including a bad speed sensor, vacuum leaks (on some models), or a failing control module.
Troubleshooting Steps:
1. Check the fuses: This is the easiest and first thing to do. Replace any blown fuses with the correct amperage.
2. Inspect the brake lights: Are all three brake lights (two on the rear, one on the center high-mounted stop lamp) working? If not, replace the burned-out bulb(s).
3. Test the brake light switch: This is usually located near the brake pedal. You may need to manually push it and observe if your brake lights come on. If it doesn't engage, it likely needs replacement.
4. Diagnose the Cruise Control: This is more complex. Possible problems include:
* Low brake fluid: The cruise control system might disable if the brake fluid is low (this is a safety feature).
* Speed sensor issue: A malfunctioning speed sensor will prevent the cruise control from functioning.
* Vacuum leak (if applicable to your model): This is less common in newer Avalanche models but could be an issue with older ones.
* Cruise control module failure: This is a more serious problem that may require professional diagnosis and repair.
Important Note: If you are not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic for diagnosis and repair. Improper repairs can be dangerous and potentially create further issues.
