now let's see how a 3-way switch works when in action electrical current travels from the power source and arrives at the common screw on the first terminal the current will either try to pass to the traveler screw on the left or the traveler screw on the right in our example since the switch is in the down position the current passes to the traveler screw on the left and will then try to travel along the black traveler wire until it reaches the second switch if the second switch is in the up position the current will stop having nowhere to go in this case the light will be off if the switch is in the down position the arriving current will pass through to the common terminal screw and continue out to illuminate the light the same will work at the electrical current arriving to switch number one's common screw finds that the switch is in the up position the current will attempt to pass to the right traveler terminal screw and will try to continue along the red traveler wire when it reaches the second terminal it will stop if the switch is in the down position if the switch is in the up position the current will pass through to the common terminal and then out to illuminate the light