What colour is your LED?
The schematic says that it should have a forward voltage drop of more than 2.5V. That rules out red and most new forms of white.
An old blue one might work.
Also i find said circuit kinda consfusing and thats rare :-/
Me too, it is a most odd thing.
Measure the voltage you are getting on your wiper, does it adjust from 0 right up to the supply? If it does your pot and wiring is fine.
What it SHOULD do is to light the led when voltage hit and drops below 2.5v
I don't think so. If the voltage is below 2.5V and that is the forward volts drop of the LED then by definition the LED can not come on.