Knob and Tube 3 way light question


Old 10-02-18, 12:51 PM
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Knob and Tube 3 way light question

Hello all. I need to know how to wire this situation safely and properly.
Wiring diagram below via URL.

Situation -
A friend has an old house with K&T in it. By the front door is a dual box for light switches. The left set of wires operates the porch light. The right pair operates an interior staircase light. Also, this pair links to another dual box right near that staircase light. Allowing both switches to operate this interior staircase light. All of these wires are affected by the same circuit breaker and if I connect only the red/yellow pair to a single pole switch, the porch light operates but the other wires are dead and have no power. Red is HOT/LINE.

A different person was working on it but never finished. All the switches were removed and thrown out and boxes left empty. All the wires inside are black. I don't know what the original wiring was or what kinds of switches were in there but I do know it functioned properly. The owner just wants to update to nicer switches (Leviton Decora) and cover plate.

Using my diagram as a legend, please tell me how I can wire this correctly? What kind of switches do I need? I am familiar with modern wiring and can wire a 3way switch, etc. I don't know what to do with K&T and I want to make sure I do it right.

Thanks in advance.

Wiring Diagram
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Old 10-03-18, 06:44 AM
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If the downstairs dual box containing the switch for the porch light has only 4 wires entering/exiting, then the line power for the upstairs light must come from the dual box downstairs as 3-way switches require 3 wires . Determine which of the red/yellow pair is live with the porch light switch on/off. The wire that is always live needs to be pigtailed to the source terminal of the 3-way switch in the downstairs dual box for the upstairs light. I am assuming the upstairs 3-way switch is wired correctly.
Old 10-03-18, 08:58 AM
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Last edited by AllanJ; 10-03-18 at 09:26 AM.
Old 10-03-18, 11:45 AM
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Thanks for the assist Beezlebob
As I said in my op, the RED line in the diagram is definitely HOT. There are no old switches for reference as the last guy threw them out and never recorded how it was wired so I'm clueless. I THINK (lol) he said the "RED/hot" wire was connected to the porch switch, then extended over and connected to the other switch.

Do I need two single pole switches? A single and a 3way? Two 3way switches? Can I strip some Romex and use the black wire to connect hot to hot between switches?

I was thinking this should work and be safe -
I could connect RED to source on a single pole switch, connect a length of black Romex from that source to source on a 3way switch then hook BLUE and PURPLE to the traveler posts.

Does that seem correct?
Old 10-03-18, 07:36 PM
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So if red is hot then you can use some black wire (romex ok) to make two tails. Connect one to the common (dark) screw of the three way switch and the other to one screw of a single pole switch. Connect the two travelers to the brass screws on the three way switch. Apparently the yellow wire goes to the remaining single pole switch screw.
Old 10-04-18, 11:55 AM
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Thanks PJmax
You are correct. Red is hot (source) and yellow goes to the porch light. OK, so my assumption was correct. I wanted to make sure that was safe. I know you can't/shouldn't extend K&T but was pretty sure bridging two switches with Romex would be OK. No choice really. The K&T is barely long enough to work with as it is.

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