4 pin flat trailer plug test device, insert the test device into the trailer, check the tail lights, brake lights and turn signals and check the faulty area according to the LED lights < p>The 4-way trailer tester is made from premium quality materials which are wear-resistant, sturdy and durable. It can be used for a long time to maintain safe and stable contact, and is easy to grip. The rear end has a mouth that can be hung on your key ring, lightweight and comfortable The trailer wiring harness tester is easy to use, and for each electrical function, the LED lights up. turns on and displays a good signal. Insert the trailer tester into the vehicle socket, turn on the LED signal to check it The trailer test adapter does not require any tools for Plug and Play and does not require anything else to test trailer wiring harness efficiently. Double-sided design The trailer wiring tester is suitable for all types of trailers, including boat trailers, horse trailers, ATV trailers and multi-purpose clutch devices for trailers. cargo