Abstract: A system is disclosed for testing electrical devices on a trailer without a truck being connected to the trailer. The system includes a control cable and a test control box. When an operator activates the test system, the box selectively powers a number of different electrical devices on the trailer through the control cable. As the different devices are powered up, the operator is able to physically inspect the trailer to be sure that each device works or does not work. The system may include one or more closed circuit cameras and a display screen operatively engaged therewith. Each camera is positioned to capture an image of one of the electrical devices and to transmit that image to the display screen where it is viewable by the operator. The cameras and screen allow the operator to remain in a single location while testing all of the devices on the trailer.