Ran across this LED the other day, since then have found two more just like this one. Let's see if you can spot the problem with this LED. I'll add some pics and explain below. (Hopefully the pictures are clear enough to see the problem.)
Normally the flat side of the LED (with the shortest lead) is the negative side. The opposite side (round) with the longest lead is normally the positive. The three LEDs I ran across were not made that way. The long lead was on the side with the flat spot, just opposite of the way it's expected to be.
I tested the LEDs to verify the polarity for proper wiring. The long lead was positive as it should be. The problem was with the lens and the flat spot being on the wrong side.
Not that I have seen all that many LEDs, but I've never run across any like this before. Thought this might be of interest to anyone here that works with LEDs in their train or layout projects.
Next time you have one that doesn't work and all appears to be correct, check the polarity.