The hot wire and traveler wire behave oddly in a three-way switch in a 1950s house. The metal box has three wires - red, white and yellow.
The red-color wire measured 116V, so I assumed it's the hot wire. The white and yellow wires measured 4-6V when not connected to anything, so I assumed they are the traveler wires. I connected the red wire to the black common screw, and connected the white and yellow to brass traveler screws.
The switch worked, except that the light turned ON when I flipped the switch OFF and turned OFF when I flipped the switch ON. I measured the voltage on traveler wires - the ON wire fluctuated between 25 and 30V, the OFF wire had 0V. I measured with a regular multimeter, with its black lead grounded to the metal circuit box.
Then I re-connected the white and yellow wires to the opposite brass screws. Now the light worked normally - turned on when I flipped on the switch and turned off when I flipped off the switch.
Can someone help with these three puzzles:
1) Why is the hot wire red instead of white or black?
2) Is white wire really a traveler wire?
2) Why does flipping white and yellow wires to the opposite brass traveler screws change the switch behavior?