This trailer tester can help you to quickly check the circuit failure of both vehicles and the 12V electrical system on trailers. Simply insert the lighting and cable tester into the socket or plug to be tested, press the test button and a clear diagnosis is made via the LED display. It is easy to use and practical. The 12V tester is connected to the trailer's 7-hole plug on one end and to the car's 7-hole socket on the other. The tester's signal light will quickly show whether the trailer or car coil is connected properly. Suitable for 7-pin connectors. Indicates failures in the vehicle or trailer circuit. Portable, easy to store, hand-held design. perfect in the commercial and private sector, for workshops, car and trailer rental, accessory trade, etc. Adapter: 7-pin Voltage: 12V size:19.7x5.3x4.3cm Material: ABS + copper colour:Black Package Contents: 1 x Trailer Tester 2 x Adapter Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.