Wiring X10 3way switches?

I bought some X10 3 way dimmer switches (both master and slave) and the wiring diagram is pretty straight forward it says to connect on wire to the load and one wire the other two that got to the slave switch to the corresponding wires on the switches. Only thing is I don't know which wires go to what in my house. Like which one the common to the load and which ones are the traveller wires. if anyone can help me that would be awesome.