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In an '80s Canadian house I took out a wall switch and now I can't figure out how to rewire it.

The box has three cables coming into it. They all come off the same panel breaker. Two of the cables have a white, a red, and a black wire. One has a white and a black. All of the white wires are joined together. So I have three loose black wires and two loose red wires. I'll call them B1, B2, B3, R1, and R2. I tested joining them and found the following:

  • B1+R1 = ceiling lamp which I want to switch
  • B1+R2 = a wall socket
  • B1+B2 = two other wall sockets
  • I don't know what the third black wire does.

So I guess I need to twist together B1+R2+B2 on one side of the single pole switch and R1 on the other side. And I guess just terminate the unknown black wire with a twist-on wire connector?

Questions:

  • Is the above the way to go?
  • I don't like trying to twist three solid wires together and attach them to one pole. It seems very insecure. Is there a switch that has multiple screws on one side?
  • How would I find out what the odd black wire is for?
2

First, you can only connect one wire to a screw. If you need to connect multiple, then you create a pigtail by cutting a short piece of wire and attaching one end to the screw, and the other end is connected to the other wires with a wire nut.

Second, you need to figure out which cable provides the power to the box. Most likely it is the cable without the red wire.

Once you know which cable provides the power, then any black or red wire you want powered all the time gets connected to this black wire with a wirenut. You should also pigtail this wire to one of the terminals on your switch. Any red or black wire that you want controlled by the switch should be connected to the other screw of the switch, with a pigtail if necessary.

In general, ceiling lights with black and red wires are wired so that the black wire is for a light and the red wire is for a ceiling fan. Similarly, the black wire to an outlet typically provides continuous power, while the red wire is connected to a switch. In either case, if the red wire is unused, then you should wirenut both ends.

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The answer to question 2 is that you are right to not feel comfortable about doing that.

Get a short bit of wire, twist one end of it together with the other 3 wires together, and put the open end under the screw. Known as a 'pigtail' among electricians.

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