Tow Ready 5-Flat Car End Tester by Draw-Tite, Hidden Hitch and Reese
A circuit tester that plugs into the 5-way trailer connector on the vehicle. The lights let you know what functions (brake, turn, tail, reverse, and stop) are working properly and what functions aren't. Inline circuit tester allows you to plug the trailer connector in on the other side.
20115 Tow Ready 5-Flat Circuit Tester