I have a 3 way switch that stopped working. What is really confusing me is how the circuit is being electrified. I thought the power was coming in through the fixture, flowed to the switch, then would either connect to the neutral or not depending on the switches were set on the travelers. What make me think the power should be coming in from the fixture I opened the wiring to the light and tested the circuit there was power on the circuit. So I thought it had to be a bad switch, what else could it be the light worked, now it doesn't, and I haven't changed any of the wiring. So what I read was whenever you change a switch on a three way circuit you should change both switches cause the other switch will probably fail soon. So I pulled both switches then tested each of the 3 wires entering each box for power. What I expected was to find 1 hot wire, and all the rest dead. But what I actually found was that all there of wires in 1 box were electrified, and two wires on the other box. I was just using a light tester, my voltmeter seems to have died on me. The light was dim on each of the wires I tested. I tested each wire by touching probe to the bare wire and the second probe to the neutral on my trouble light cord. So how can these wires possibly all have power on them, two of these wires have to be runners how they possibly have power.

I think I understand how a 3 way switch works, but this is something that is really different then a textbook wiring apparently. Anything anybody can tell me regarding what I should test next would be greatly appreciated.

If the power comes to the ceiling box, the neutral goes to the light and the other neutral, in the running wire, is retasked for power. There are only 2 basic configurations, power to the light box or power through the switches. However, you can have switches split by the box or both on 1 side. I always use a wiring book to make sure.

A 3 way switch is actually simple once you realize that the two carrier wires aren't part of the feed connection. I'm not sure what you want to know. If you have a bad switch, change it. You can certainly change both switches if you want. But if you want to trace the circuitry, open up the fixture as well and see what goes where. I'll assume you are dealing with cable rather than individual wires in conduit. That gets confusing because suddenly a neutral wire (color) is a hot wire. When troubleshooting a circuit that is unfamiliar to me I turn off the circuit and leave the traveler wires in place and disconnect the rest. It makes it easy to determine where the feed is actually coming from.

There is five ways to wire a set of 3-way switches.