Logic inside a 3 or 4 way light switch?
A "3-way" switch is SPDT. A "4-way" switch is DPDT inside. They're used like this:







simulate this circuit &ndash; Schematic created using CircuitLab

The 4-way switch is simply crossing the connections, or connecting them straight through &mdash; sort of an XOR function.

If you only need two switches, just connect SW1 and SW2 directly to each other. If you need 3 or more switches, add any number of 4-way switches in between as shown.