A circuit assembly for simulating a load current from an on-board network having an input connected to a line of the on-board network of a vehicle for connecting to a load, an output connected to a light source which replaces the load. A series circuit formed by a resistor and a switch, wherein the resistor has a resistance in the same order as that of the load to be simulated, and the series circuit is connected in parallel with the input. A switching controller with the input connected in parallel to the input of the circuit assembly, and draws a current from the line of the on-board network for connecting to a load smaller than the load current of the load to be replaced. The circuit assembly is open the switch and actuate the switching controller and to close the switch and deactivate the switching controller.