Faust;
Late 122 /123 Wiring Diagram:
http://www.sw-em.com/123GT-Wiring-Diagram_Euro.jpg See Ign Sw at Item 52
Headlights are
not supplied by Ignition Power, they are supplied by Black wire, connected to Battery Power terminal (30). If you were to connect that wire to term 54, Lights current would run through Ign Sw contacts...not recommended!
If you want to make a change, to make lights an Ign Sw controlled function, you must install an Ign Slave Relay. See:
http://www.sw-em.com/Ignition_Slave_Relay.htm
Cheers