Trailer plug tester
This 7 pin tester indicates failures in the wiring on both towing vehicles and trailers/caravans etc. Just plug the tester in the 7 pin socket or the 7 pin plug of the trailer or caravan and press the yellow button on the side of the tester. When the wiring is good, all the LEDs light up. If there is a failure - the affected cable will light up at the display (color of cable and function).