The green or uninsulated ground wire always goes to this ground terminal. Dan Harmon more. You will need to install the new 4 way switch in between the two 3 way switch. If the current is followed Instructions and diagrams are available here:
Thanks to the both of you for the comment; it helps to know that you find the information useful.
Help wiring a 3 way switch
In this 3-way switch wiring diagram, the power-in line enters the light box, but 3 rope cables are then installed between the light box and each switch box. Two rope. See Actual Switch Box Wiring. Here it is again: No, I didn't disable any printing. Commonly called a "fuse box," it may contain either circuit breakers or fuses. This isnt really a comment more of a question.