3 Way Switch Common Wire. Only one of them is important to identify for the purposes of replacement. the common TERMINAL. Three-way switches are also common in hallways, garages, and kitchens.
Check the operation of your light. Three-way switches are always used in pairs. The third wire that was never live is the one that connects to the common (black) screw.
Three-way light switches are ideal when you need to control lights from two locations.
Wall switches used to control ceiling light fixtures or other fixtures come in three types.
The two grounds are connected together and then to the green. Of the three circuit terminals, one is called the common and the other two are known as travelers. Turn power off, connect wires, mount switch into box, turn I think somebody wired it wrong at one point because the light doesnt toggle like it should.