Adding back removed 3-way switch from 4-way setup
Power off. 
Pick any 2 of the capped wires formerly attached to the 3-way.  
Nut those two together. 
Leave the third wire nutted independently. 
Power on. 
Throw any other switch in the 3/4 way group.  Does the light turn on or off? 


all other 3/4-ways work correctly -- fail*. Pick a different pair and go to 1. 
lights do not work in either position -- success. The two nutted together are the messengers.  



Mark both messengers with yellow tape (or other appropriate marking) -- messengers are interchangeable, so you don't need to distinguish them from each other.  

The two messengers go on the brass screws of the 3-way switch.   

The remaining wire is common and goes on the black screw.  

* Or, if you just want to eliminate that 3-way, you can stop right here and you are done.