Abstract: A trailer light tester for supplying DC current to at least one circuit in a trailer where a seven pin female connector is rigidly and securely attached to a side or rear panel of the trailer light tester wherein, when the seven pin female connector which is rigidly and securely attached to the light tester is connected to the seven pin male connector which is rigidly and securely attached to the front end of the body of a truck trailer, the light tester is rigidly and securely attached to and is fully supported by the seven pin connector attached to the body of the truck trailer and projects out from the front end of the truck trailer body without requiring any additional support.