Q: Brake lights not working in 2001 Mercedes-Benz SLK320

If both brake lights are out, you might be having an issue with your "BOO" or brake on/off switch. This is the switch that actually detects when you’re stepping on the brake pedal and sends the electrical signal to the lights. One things that is sometimes used to narrow down things is to try to turn on your cruise control. Usually if the BOO is not working, your cruise control won’t engage either. This is because it uses the signal from the switch to cancel when you step on the brake. If there is a problem with the switch it simply wont engage. I would certainly suggest seeking the aid of a professional mechanic, such as one from YourMechanic, to accurately diagnose your brake light issue. This is especially important since driving without brake lights is a safety issue.