Abstract: A trailer electrical connector system for a motor vehicle includes a housing configured to be connected to the motor vehicle, a plurality of electrical connectors each configured to connect to a plug-in trailer connector to provide electrical power to a trailer, and a normally closed switch electrically coupled to a pair of the electrical connectors, wherein the normally closed switch is in a closed state when the plug-in trailer connector is not connected to the plurality of electrical connectors and moves to an open state when the plug-in electrical connector is connected to the electrical connectors. The system also includes a controller sensing an electrical signal across the pair of electrical connectors through the normally closed switch and detecting a state of the electrical connection of the trailer to the vehicle based on the detected state.