This switch is a small electrical component that tells the car when the brake pedal is pressed. When it fails, it can remain "closed" (as if the brake pedal is always pressed), causing the brake lights to stay on, and disabling safety features that rely on knowing the brakes aren't applied, like cruise control. The constant drain on the battery from the lights could also be why the cruise control is not functioning (low voltage).
Other less likely possibilities include:
* Faulty wiring: A short circuit or damaged wiring in the brake light circuit could also cause the lights to stay on. This could also affect the cruise control system.
* Brake light fuse: While less likely since the lights are staying on, a faulty fuse could exhibit odd behavior. Check the fuse box.
Troubleshooting Steps:
1. Check the brake light switch: This is the most probable cause. It's usually located near the brake pedal itself. You may need to look under the dash. You can sometimes visually inspect it for damage. A simple test involves disconnecting the switch to see if the brake lights turn off. If they do, the switch is definitely the culprit. *Caution:* Disconnecting it means you won't have brake lights, so only do this if you're in a safe location.
2. Check the brake light fuses: Locate the fuse box (usually under the hood or dash) and check the fuses associated with the brake lights.
3. Inspect the wiring: Look for any frayed, melted, or damaged wiring around the brake pedal and related components. This is more difficult and requires some electrical knowledge.
4. Battery Voltage: A very low battery voltage could also cause issues, especially with electronics like the cruise control, although the brake lights staying on are a more likely culprit of the low voltage.
It's generally recommended to replace the brake light switch if you suspect it's faulty. It's a relatively inexpensive and easy repair for a mechanic or even a reasonably handy DIYer. However, if you are uncomfortable working with car electrical systems, take it to a qualified mechanic to diagnose and repair the issue safely. Leaving the brake lights on will drain your battery.
