Could it have something to do with the leads going through the old holes? Could there be residual metal in there that would cause a short?
Another possibly related problem, when I turn the unit to the side (the top is perpendicular to the ground), …
This didn't work... Could there be a problem somewhere else that would prevent only light 15 from lighting up? There's continuity between all of the points on each wire so it's properly soldered, and I know the polarity of the LED is correct.
Thanks for the quick replies, guys. Both pads are gone, so I'll solder the negative lead to the RLED pad and wire the positive lead to pin 1 of that chip. The wiring diagram was exactly what I needed.
I'll give this a go tomorrow and I'll update.