replacing an old 3-way switch (the old one has no labeled common terminal)

[IHateMyJob2004]

OK, I'm replacing a 3-way switch. I pulled the old one out (still connected to the wires) and the common terminal is not labeled. How do I know what terminal is common?

The only thing I can find to a brand is A-H&H. The switch is probably 40 years old.

EDIT: The old switch has the quick install tabs onl. No screws, so no color coded screw.

 

[IHateMyJob2004]

The old switch was easy to take apart. I figured out how it worked. Resolved.

 

[ktehmok]

Just in case you don't have the switch to take apart, here's how to determine the common:

Take the 3 wires (2 travelers & the common) & separate them, turn the power on. Touch one wire to the other. By process of elimination, one wire will turn on the light when touched to the other two (You'll need to flip the switch at the other end of the 3 way between tries, assuming it is hooked up correctly). If you're too chickenshit to do this with the power on, use a volt meter between the wires and it will show resistance when the correct wire is touched.

Mark the common with tape or a sharpie so the next guy will know.