Brake light harness from the cab interior to the 3rd brake light,  This kit provides four wires,  Circuit One ( Yellow), Circuit Two (Blue), Circuit Three ( White for Reverese), Ground (Black) . This kit includes a diode to allow the reverse to turn on the cargo light if your aftermarket third brake is so equiped.   This kit includes a flash controler that will will strob,  show solid ambers and work in conjustion with your brake and turn signals.   Recomend that 3 switches be used.  Minimum 2 switch option is avaialbe with how you your it and use the unit.