Imagine a bicycle light.
The track has a voltage difference between each track when live.
The led is connected across them.
You can actually hold an led across the track and get a light. The polarity must be right for a diode to emit light and thus there is a need for two diodes.
Here are the results of a few experiments. It is done using a 5V diode and will light with ac (on/off so many times it looks like continuously on) and dc if the polarity is right. With a lot of wiring (I must look into it) the leds could be a way to setting up the control panel with lights to indicate not only if the track is live but in which direction the current is running. This is one in the eye for dcc (sort of) and is part of the fun of trying to control (or at least know what's going on in) the analog layouts. It could give a realistic control panel.
Here goes. The photo below is the circuit where the 16 V ac is used to light the diode (momentarily while the point motor is changed). Pressing the momentary switch (actual term) the point motor switches and the diode lights. I haven't shown it but you need another switch and diode to do the other direction (i.e switch the point back)
off
on
Then if you do two diodes back to back (with both different polarities it will tell you when the track is
not live
in the forward direction
and the reverse direction
I wll draw up these circuits (Gawd give me time)
and post them here
and if I manage to get my blog going (Help administrators, I can't get my blog to open)
I'll try to develop the theme.
It might make a very useful control panel but would be a mess of wires
Maybe needs some thought
Onwards