Abstract: A tailgate sensor system for providing a warning signal to a driver of a pickup truck when the tailgate is not in a closed position. The tailgate sensor system includes a detector mounted on an exterior of a pickup truck, an activator mounted on and moveable with a tailgate of the pickup truck, and a signal generator in communication with the detector. The detector is positioned relative a range of motion of the activator such that a signal is generator by the detector and received by the signal generator when the tailgate is in at least a partially open position. Upon receipt of the signal, the signal generator generates a warning signal to the driver.