Our easy-to-use circuit tester helps you quickly identify and fix problems with your trailer light circuit. Simply plug it into the bumper connection or in-line between the tow vehicle and trailer, turn on the lights to be tested and check the LED lights on the tester. The correct LED will be illuminated if the power and ground wiring of the tow vehicle is functioning correctly. STRAIGHTFORWARD TRAILER LIGHT TESTING - Simply plug the tester inline between the tow vehicle and trailer, turn on the lights and check the easy to read LEDs. ISOLATE PROBLEMS QUICKLY- By effectively splitting the trailer wiring harness in half, problems can be quickly traced to the tow vehicle side or the trailer side wiring. NO TOOLS NEEDED - Plug-n-play design means you don't need anything else to effectively test your trailer light harness. LONG LASTING CONSTRUCTION - Designed to be weather, corrosion, and impact resistant for years of reliable service. CONVENIENT COMPACT DESIGN -The two-sided design means you can leave it plugged in or store it conveniently in your glove box, door pocket, or tool box.