Method for switching a vehicle lighting system

The method involves implementing test routine (R) in a light control unit (10) for verification of signal processing in the light control unit. Voltage at an additional signal input (21) is monitored, and the test routine is started, during first time lying of vehicle-supply voltage at the additional signal input. The starting of the test routine is stopped, when a driver sided switching signal exists at one of signal inputs (5.1-5.3). The test routine is again started, after termination of the driver sided switching signal, which lies on a level of the vehicle-supply voltage.