The ENSTO KKLS1 is a simple light control that turns on during the dark hours (adjustable 5-20lux or so). If it stops working it is often because a Zener diode in the power supply part has become short circuit. Sometimes there is visible heat damage on the PCB, but often the diode just dies. The original diode is probably a 1.3W 24V component, it can be replaced by series connected Zener diodes that make 24V total. Here two 12V diodes are used, they tolerate more overload than the original and also the wires between them are uncut to help heat dissipation. Check the orientation of the diode(s), it points in the same direction as the 1N4007 diodes on each side of the Zener. Other less common faults are the relay driver transistor, the relay coil, contacts or soldering connections.