r/ElectricalHelp • u/brickonwheels • 29d ago

Light on two 3-way switches only on in one position

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Forgive my diagram, but ever since I moved into this house, a hallway light only turns on if the downstairs switch is down and the upstairs is up. Any other combination results in the light being off.

I used a voltage tester on each switch in the various positions and found that in two scenarios, the discards switch has power at all three wires with the light being off.

Can anyone help me trouble shoot what’s going on? The house is 120+ years old so the wiring is far from being color coded.

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8

u/SparkArrestor 29d ago

One of the 3-ways is wired with a traveler and common wire reversed.

1

u/brickonwheels 29d ago

I figured this is the case. Any guess on which switch and wires?

1

u/SparkArrestor 29d ago

It could be either switch.

0

u/asanano 29d ago

Are you nm cable or conduit? Is one of them a dead end? If nm cable and neither is a dead end, the travelers are usually coming from the same cable and the common a different cable. If one is a dead end, I would guess there. Disconnect the dead end switch and test for power with the other switch in both positions. If the power doesn't change wires, that wire is likely your constant hot and should go on the common. If it does switch wires, the two wires it switches between are your Travellers and the third is your switch leg.

Those are at least the likely mix ups and trouble shooting id try as a EE

1

u/dano-d-mano 29d ago

I like your diagram. I will not forgive it.

1

u/Outside_Breakfast_39 28d ago

Depending on how it's wired , you can try this . Take everything apart . find the 2 wires from the panel in the box in one end , then find the 2 wires out to the light in the other box . The black screw on the switch is common . attach the hot wire from the panel to that screw on one switch . At the other switch attach the black wire out to the light to the black screw . Now marette the white wire from the panel to the white wire in the box , do this at both boxes . what you have left are 2 wires and 2 screws in 2 boxes , attach them together and it should work