On Sat, 25 Aug 2012 13:12:44 -0700 (PDT), NT wrote:

a filament lamp consumes about 8x run current during starting, so
you'd need a more complex circuit to avoid frying the led. bridge
rectifier, zener, resistor, led.

True enough but not for very long and LEDs can take a hefty overload for
short periods. Might get away with it, or not... B-)

If you are going to stick something in series back to back 5W zeners of
suitable voltage (both) would probably be better, no risk of a larger
than expected current draw frying the LED. I don't like the power
dissipation in either the series R or back to back zeners.

We don't know te topology of the wiring which switch of the three is the
intermediate, which is the live end and which is the load end of the two
way circuit.

A small mains transformer (recovered from an old wallwart?) wired across
the light with a bit of bell wire (as it's LV and isolated) to a convient
indicator. I know breaks the don't want to run a wire part of the spec.

--
Cheers
Dave.