This Attwood Trailer Light Circuit Tester reliably identifies which circuits in a trailer's electrical wiring are having issues. This inline tester plugs into the wiring harness and an indicator light is illuminated if a circuit is faulty. This tester can help identify issues with the circuit to the taillights, the ground, and the left and right turn signals. Attwood Corporation has been an award-winning leader in engineering, testing, and manufacturing the highest quality marine products for over 100 years. We deliver safe and reliable lighting, fuel systems, water systems, seating & pedestals, swim ladders, custom upholstery, and general marine accessories that are easy to install and meet regulatory compliance.