I had a track that energized accessories, but did not uncouple cars intermittently - then finally quit altogether. Yesterday, I got around to pulling it and installing another one. Checked the bad one, all looked good. Meter showed an open on the wire in the red circle below, but again, all looked good.
So, I started to try to pull the wire out of the black shrink wrap.....started to pull out real easy! It had broken loose in the wrap. Took the wrap off, stripped and re-soldered, wrapped it - and all worked fine.
Posted just in case anyone else runs into the same problem.
Greg