A method for controlling a multi-color signal assembly with a multi-color LED, a connection for voltage supply, and a control input. The control input is connected to a control output of a first control unit for controlling the signal assembly by pulse-width modulation signals (PWM signals) or to a signal assembly control output by the bus communication. After a supply voltage UB is connected, voltage UDI/BUS at the control input is measured within a predetermined time span Δt, wherein the first and second control units have respective first and second voltages at the control input within the time span Δt, wherein the first and second voltage are different. The signal assembly is placed in a BUS mode or in a PWM mode depending on the measured voltage UDI/BUS, can be controlled by bus communication in the BUS mode, and can be controlled by PWM signals in the PWM mode.