To control 1 lamp from 3 locations, you use2 three-way switches (S3W)1 four-way switch (S4W) in the middleWiring ProcedureConnect the power source to the common terminal of the first three-way switch.Connect its travelers to the two terminals of the four-way switch.Connect the other side of the four-way switch to the travelers of the second three-way switch.The common terminal of the last three-way goes to the lamp.Then the neutral wire completes the circuit to the lamp.This setup allows control of the same light from three different places.