Abstract: A universal trailer lighting adapter permits connection of the lighting systems of American trailers to either American or foreign motor vehicles. Circuitry employing complementary metal oxide semiconductor logic elements in cooperation with solid state switches results in negligible current drain from the motor vehicle battery when the motor vehicle is not in use. The circuitry is powered directly from the battery of the motor vehicle, thereby eliminating additional loading of the motor vehicle electrical components and wiring and assuring full brightness of on both the motor vehicle and the trailer. The circuitry is fused or current limited to protect the electrical systems of both the motor vehicle and trailer from shorts that may occur in the trailer lighting system. A light emitting diode is provided to indicate a malfunction in either the adapter circuitry or the trailer lighting system to the driver of the motor vehicle.