Removing Dimmer Switch, 3 wires
Identify which two wires are the messengers and which is the common. 


You would rely on markings on the old dimmer switch for that.   

You can also look in the back of the box to see how the wires group in conduit or cable: if two are in one cable and the third is not, the two together are the messengers. 


Join one messenger and the common.  


If the other switch(es) now turn on in a position you don't like, use the other messenger. 


Cap off the unused messenger. 


It will be hot whenever the light is off!!!