The-test case for trailer lighting is used to quickly and easily check the 24 V lighting on a truck trailer without the need for a matching truck. The unit has integrated sockets for seven-pin trailer plugs N+S. In addition, it has the 13- and 15-pin sockets for trailer lighting and for ABS/EBS. The power supply for the tester for quick and fast testing is provided by a 230 V power supply unit supplied. The trailer tester quickly detects all electrical interruptions. All lighting functions can be called up by simulating voltage via a rotary switch. LED indicator lights reliably show the functional readiness of the rear lights when the switch is turned. If there is an interruption somewhere, be it a broken cable, a loose jam or a burnt-out tail light bulb, the control LED will not light up.