Conventional 3-way wiring is not very complex. However there is an alternate wiring configuration that could cause confusion. This alternate configuration has been known as “California” or “West Coast” wiring. With conventional wiring, the line (120 volts) connects to the common of one switch, while the load (light) connects to the other switch.
With the alternate 3-way wiring configuration, the travelers are connected together (same as conventional wiring) and the line is connected to one of the travelers at one of the switch locations. The commons are connected together and the load is connected to the commons at one switch location. It can be difficult to determine which configuration is present in a 3-way wiring configuration. When replacing a switch, the new switch needs to be connected the same way as the old one. Again, if you have any problems with these switches, it may be best to call an electrician.