If you disconnect all six wires, at one of the locations you will have one
hot wire. It is the common on that side and the two travelers go to either
of the other screws. After you connect the wires on that switch, check the
three wires at the second location. One will now be hot. It is a traveler.
Flip the installed switch to the other position. You will now have a
different wire that is hot at the second location. It is your second
traveler. The remaining wire is the common which goes to the light



"Steve" wrote in message
. 142...
I have 2 3 way swithces off from a 75 year old house. All three wires are
black, and I don't know which one is the common wire. Is there any way to
find out? And does it matter which screws the other 2 wires are attached
to if you have the correct common wire? Right now I have it hooked up and
it works on both switches, sometimes..