72V nominal, is this for railway work?
Here is a circuit I designed a while back, originally for 50v (that was tested and worked) but the values in this version are for 100v (so far not tested).
I don't think it will suit you as is because it doesn't have a remote indicator LED and also the threshold is very low at just a few volts because in our application anything from about 4-5V to 100V is "on". But it may offer a different approach worth looking into.
Basically the constant current source (20mA) fixes the large range of currents over a 0-100v range you get using resistors, after that it's just a matter of choosing LEDs/diodes that are happy with 20mA.
Rob
