Locate the Orange wire, at position H, on the headlight switch. Connect a wire from this point to the Common of a new relay. Connect a wire from the Normaly Closed terminal of the relay, this wire will be mentioned later. Locate the Brown wire, at position S, on the headlight switch and connect it to the coil of the relay and ground the other side of the coil.

Locate the Brown wire that goes into the trailer plug. Cut this wire, connect 2 different color wires to each of the cut wire ends and bring them into the cab were you will locate your new double pole double throw push button switch. Connect the wire that comes from the trailer plug side of the cut wire to a Normaly Closed and to a Normaly Open terminal of the new switch. Connect the wire that comes from the tail light side of the cut wire to the Common terminal of the switch that has a wire connected to the Normaly Closed terminal on the switch.

Now back to the wire we left behind. Connect it to the Common terminal of the switch that has a wire from the trailer plug connected to it's Normaly Open terminal.

Once completed the trailer tail lights will flash if you press the switch during the Day while the tail lights are off and it will flash the trailer tail lights at Night while the tail lights are on.