In this case, the wires from the power source may enter the light fixture box first, then it goes into one switch box and then the other. In this type of wiring, the inbound white wire connects to the light fixture without any interruption. The black wire then connects to the taped white wire that goes from switch one and then connects to the common terminal in switch two. Red and black travelers then connect paired traveler terminals on both switches.
In building wiring, multiway switching is the interconnection of two or more electrical switches to control an electrical load from more than one location. A common application is in lighting, where it allows the control of lamps from multiple locations, for example, in a hallway, stairwell, or large room.
In contrast to a simple light switch, a single-pole, single-throw (SPST) switch, multiway switching uses buttons with one or more additional contacts, and two or more wires are run between the switches. When the load is controlled from only two points, single-pole, double-throw (SPDT) switches are used. Double pole, double throw (DPDT) switches allow control from three or more locations.
In alternative designs, low-voltage relay or electronic controls can switch electrical loads, sometimes without the extra power wires.