Tinksky 7-pin 12V Towing Horsebox Caravan Car Truck Vehicle Light Electrics Diagnostic Tester Unit Plug Socket Can be used on many Applications fitted with Unit N 7 pin plugs and sockets generally fitted on Trailers, Caravans, Cars, Truck, 4x4's etc. Designed to indicate a faulty wiring or blown bulbslight in the wiring on your trailer, caravan or horsebox with a Six Light LED system. Quick, easy and very simple to use! Just plug the tester in the 7 pin socket or the 7 pin plug of the TrailerCaravan and press the yellow button on the side of the tester. If the wring is good, all the LEDs light up. Comes with instructions. Portable and easy to store. Makes checking the wiring of your car, trailer, caravan horsebox easily before you set off on your trips or travel. Powered by 9v Battery which is not included in package, but you can buy it from local store easily.