A system according to claim 14 including means for putting the coupler into service or withdrawing it from service, said coupler having, on the one hand, a start key (BMS) to set a bistable flip-flop (BB8) whose input is connected to a coupler command input (CMD), whose output is connected to a letting in call gate (P75) and to a power circuit gate (P88) of an unused signalling lamp (SHS), on the