an embodiment which differs mainly from the embodiment of fig1 with regard to the components of the flashing circuit controlled by the pulse signals of the central pulse generator with its oscillator 10 in fig2 as soon as the directional switch 20 is moved to the operating position l or r the pulse generator 10 supplies pulses to a circuit path which extends from terminal 15 through the changeover switch contact 202 outputs 49 and the electro magnetic relay s the relay s pulses periodically synchronously encloses the lamp circuit with its make contact s a relay k in series with the lamp circuit performs a a monitoring function as long as both lamps bl or br are lit the current through the relay k is large enough to energize it the relay is slugged that is it is provided with a means for extending the energizing pulse long enough to keep its contact k closed during and between adjacent current pulses thus contact k keeps a circuit for a monitoring light kbl closed however a failure of one of the lamps bl or br reduces the current sufficiently so that the slugging effect is no longer adequate to hold the relay k in its operative condition the relay k then operates in synchronism with the pulses the relay k then pulses the circuit of the monitoring light kbl synchronously with the pulse generator so as to produce a periodic signal the operation of.