The black line wire connects to the common terminal of the first 3 way switch.
Three way light switch wiring.
When wiring a 3 way switch first screw the terminal screws of the new switch until they are difficult to turn.
Regardless of what 3 way switch wiring diagram you re following you ll need to use a 3 wire cable to connect the two 3 way light switches.
Connect the two remaining traveler wires to the two brass or light colored screws.
Hook the curled end of the wire under the screw then tighten down the screw to hold the wire firmly in place.
Connect the wire marked common to the black or dark colored screw.
In this diagram the incoming hot wire attaches to the first switch s common dark colored terminal.
So what you should see if you have correct 3 wire electrical cable romex is a black power white neutral and now a 3rd red wire.
This 3 way switch wiring diagram shows how to wire the switches and the light when the power is coming to the light switch.
Connect the ground wire to the green screw.
Installing the switches and light 1 attach the black power cable from the wall to the general screw black in the three way light switch.