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Old 12-20-2009, 10:24 PM   #1
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Wiring problem

A single-switch light fixture in my bathroom stopped working a couple weeks ago. I got a chance to try to diagnose the problem today. Here's what I found:
1. The light fixture and the light bulbs were fine: I connected it to another power source and the bulbs lit up.
2. The switch worked: I used a multimeter to conduct a continuity test on the switch. It passed.
3. The "hot" wire that went into the switch was indeed hot: My multimeter detected a voltage from the hot wire when one lead was on the wire and the other lead was on the ground.
4. The "hot" wire that went into the light fixture was cold: My multimeter didn't detect any voltage when one lead was on the wire and the other was on the ground.

These findings to me seem to show that the wire from the switch to the fixture is the culprit. Since this was my first time dealing with wiring, could the experts on this forum answer the following questions:
A. Did the tests I do conclusively find the root cause? Are there any other tests I can do to narrow down the problem area? Or point to a new possible area?
B. If my conclusion is correct, then is there any good pointer/link on how to change the hot wire there? Although the distance between the switch and the light fixture is short, the wiring is behind the wall and I don't know if it takes any "detour".
C. If I hire an electrician to fix the problem, how much time do you think this project would take?
D. How could a wire behind the wall stopped working all of a sudden?

Thank you!
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Old 12-20-2009, 10:30 PM   #2
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try hooking up your known hot circuit to the line (in) side of the switch. I have had switches that went bad. They would still carry enough load for a voltage reading but when there was a load (although a single light is not much load) the contacts would not carry the current.

or just throw in a new switch to be sure.

why would a wire in the wall go bad?

did you hear a mouse scream about the time the light quit working?

being funny but a possibility as well as:

a junction box somewhere that now has a bad connection; the wire was stapled when installed and just finally worked in to a full break;

I'm sure there are others as well.

so, is this a 1 or 2 story house? is this bath on 1st or 2nd story? basement, crawlspace, or slab?
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Old 12-21-2009, 06:29 AM   #3
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I forgot to mention that I did throw in a new switch when it first broke, and that didn't help.

This is a 3-story condo. The bathroom is on the third floor.

I don't know if this matters: The light did come back for a few short seconds a few days after it died. But it stopped working again after I flipped the switch off and on.

I didn't hear any screaming, yet.
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Old 12-21-2009, 06:53 AM   #4
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Carefully remove the incoming wires on the fixture and recheck them for voltage again with the switch in different positions.
Don't hurt to recheck and recheck multimeter setting.
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Old 12-21-2009, 08:31 AM   #5
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Are there a couple of switches and say the wires from both switches go to one cable? And is there another light or fan?

It's possible that there could be two switches, one to a fan and the other a light, but the wire goes to the fan first, then the light. And a connection at the fan which has gone bad for the light.

Or there could be another light and the wire goes there first.

Or there could be a junction box in the attic.

Or could even go to an outlet first! (People do these wiring jobs and they can be as creative as they are with other things in life...)

It is not uncommon for wiring connections to come loose.

As to an electrician, this would be an easy job, so minimum cost.
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Old 12-21-2009, 09:39 AM   #6
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Locate the neutral (white wire) connections for the fixture. They will either be in the switch box or at the fixture. Check for a loose connection.
"Life is hard. Life is harder when you're stupid." John Wayne
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Old 12-28-2009, 07:43 PM   #7
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Did you look for a short at the beginning or end of the run? Have seen this a few times
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