Replacing switch as in pic. Old Switch has no black terminal screw. How do I tell which is the common wire? Red is typically traveler wire but It has the white wire connected to terminal as well which I don’t think is common?
Use a non-contact voltage tester like this Klein from Amazon:
See which wires are live in various switch positions. Typically you will have either:
- One wire always hot = incoming hot
- The other wires alternate depending on switch position = travellers
- One wire hot only when the light is on = switched hot
- The other wires alternate depending on the other switch's position = travellers
If everything lights up an NCVT all the time (except when the breaker is off) then you'll need to test with a multimeter. Some NCVTs are more sensitive than others to phantom/induced voltage.