Methodically dealing with one wire at a time will help avoid confusion and mistakes.
Old style light switch wiring.
Probe the existing hole with a keyhole saw to find the horizontal edges of the lath.
In box 1 disconnect a wire on the old switch and attach it to the correct terminal on the new one.
We have a double switch for our bathroom that controls the extractor fan left switch of 2 and the bathroom lights right switch of 2.
The alternate 3 way switch wiring configuration california or west coast was used as a way to wire 3 way switches and be able to supply line voltage to either switch this configuration is no longer allowed as the neutral is not present in each switch box.
Here s how to do it without breaking the plaster and lath.
If the new switch s cover plate is smaller than the original you can make it easy on yourself and cover the old plate s outline with a slightly oversize new plate no wall repair or touch up paint required.
Conventional 3 way wiring is not very complex with conventional wiring the line line voltage connects to the common of one switch.
Moiak light toggle switch retro single control switchs 6a round lamp switch mounted wall light button switch old fashioned toggle switch 6 26 6.
Fix old house wiring problems.
Upgrading to a new rocker style switch takes just a few minutes and requires no extra wiring or special connections.