Some more pics from this house. (I decided not to take any of the two dead rats found in the attic! Yuk!)

This twin light switch looks innocent enough:
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But instead of a proper fixture box, behind it is just a fabricated "box" of wood:
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Several other switches were done the same way. This switch is typical 1950s/1960s style, and the cable dates to 1965 or earlier, so it's probably been like that a long time. This technique seems to have been surprisingly popular at one time, possibly because the old round "tumbler" switches were commonly mounted on a wooden surface pattress.

Another interesting piece of work came to light when I traced a cable to a receptacle and found an NM-type cable disappearing into an old length of heavy-gauge steel conduit to drop down the wall to a receptacle. The only problem was that the cable entering the conduit at the top was a different gauge to that emerging at the bottom!

I tried pulling through a new cable, expecting to find a taped splice buried in the conduit, but couldn't get it to budge. Here's what was hidden behind the plaster in the wall:
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Closer examination revealed what must have happened. The large-gauge Imperial-sized cable entering from the top must have been the original 1950s/1960s feed to an electric range. The box is typical of those used for the isolation switch (which normally incorporated a receptacle as well). The conduit then continued down the wall to where the outlet plate for connection to the range would have been.

Somebody must have replaced that outlet with a regular duplex receptacle and abandoned the old control switch. The smaller cable run down to the receptacle from this "junction box" was metric, so it must have been after 1970. To cover the old range/receptacle combination they just shoved a small piece of drywall into the box and then plastered over it. From the drywall and the style of recept below, I would guess this was done in the 1980s or later.