Owain wrote:
Ian Stirling wrote:
Into the diagonal bit of the stairs, route out a 10mm*10mm or so groove.
Drill a hole per tread in this, all the way through, aimed down at the
tread, 10mm dia, painted matt black internally.
Place a 3.5mm mono switched socket in this hole, and wire up all the
sockets in series.
molex connectors would probably be cheaper and easier than 3.5mm plugs -
see Big Clive's LED charm bracelet.

But really fiddly to put in.
The advantage of 3.5mm plugs is that they are by nature round, and hard
to get the wrong way round down a hole.

Alas, I have no stairs

By design, or did the feck-up fairy get hold of the plans between the
architect and the builder?

One floor level throughout.