It can be used on many Applications fitted with Unit N 7 pin plugs and sockets generally fitted on Trailers, Caravans, Cars, Truck etc. The Tester is designed to indicate a faulty wiring or blown bulbs/light in the wiring on your trailer, or horsebox with a Six Light . Quick, easy and very simple to use! Just plug the tester in the 7 pin socket or the 7 pin plug of the Trailer/ and press the yellow button on the side of the tester. If the wring is good, all the LEDs light up. Comes with instructions. Feature - Color: As shown. - Material: ABS and Copper. - Size: 20x5x4cm. - Bronze needle: Hpb58-2, Hpb59-1. - Item Type: Diagnostic Tools. - Battery Type: 9V (not included, please purchase additionally). - Connect the trailer 7-hole plug and the other end connects the 7-hole socket. The tester lights will quickly show whether the trailer or coil is connected properly. - Can effectively test out what’s the problem in connection, The cross slotted of size is easier to control. - Frosted surface, Safe and dependable performance, Deft appearance, convenient to use. - Designed to indicate a faulty wiring or blown bulbs/light in the wiring on your trailer, or horsebox with a Six Light . - Quick, easy and very simple to use! Package list: 3 x 7 Pin Truck Trailer Plug Socket Tester Wiring Circuit Light Test Tool Diagnostic Tools