Why do you need a brake light switch? Brake light switches are necessary only if you're installing a supplemental braking system monitor, and the vehicle's OEM brake light switch doesn't work when the vehicle is in ‘tow' mode. Both the new universal switch and our vehicle-specific switches are only activated when the brake pedal is depressed. No other manufacturer provides brake light switches with this level of specificity. Why? When you know when the towed vehicle's brake pedal is depressed and released, you know if the supplemental braking system is positioned properly and working as it should. This switch sends a beam of infrared light to detect brake pedal movement. When the pedal moves down, it sends a signal to the monitor that the brakes have been applied.