Quick Check --- This trailer hitch socket has one side to connect the 7-pin plug of a trailer and another side to connect the 7-pin plug of a car. This tester quickly indicates whether a fault is in car wiring or trailer wiring, which can effectively test the problem of 7-pin plug and socket connection. European Universal Standard - -- Passes Europe CE, ROHS Certification, ensures maximum strength and durability for long lasting use. Such a handy trailer tester tool you will need. Reliable Quality --- The 7 pin trailer tester with safe and reliable performance, reasonable design. Skillful appearance, convenient use. The trailer tester socket is widely suitable for caravans, RVs, RVs, vehicles, trucks, trailers, etc. Testing requires a 9V battery (not included) High Performance --- The automotive trailer socket tester is made of high quality ABS and copper material, frosted surface, durable and reliable, ensure resistance and maximum durability for long-lasting use. One side connects to 7 pin plug and the other side to 7 pin socket, also can be applied to 13 pin with the adapter.