Horn P005 is supplied via relay T3 of engine compartment control unit B001 from a direct line from the battery protected by fuse F10 in unit B001.The coil of the above relay is excited with a general earth signal received following closure of one of the keys on the steering wheel. They are connected to the vehicle wiring via the clock spring D047 (LOW version, steering wheel without controls) or via the Steering Wheel Node M093 and D047 (HIGH version, steering wheel with radio controls).The relay supplies the single-tone horn P005.