Those two cables will get connected to those 2 contacts of the coil of a 12V relay. Which cable goes to which side of the coil, does not matter. The ignition ON signal feeds into a fuse (I chose 10A), which goes to the "common" contact of the relay. And the outgoing cable from that relay leaves from the NC contact of the relay, i.e. the :normally closed" contact, so that the DTRL is on, when ignition is on. But if you then switch on low beam, the relay will move its contact over to the NO-contac