Well, it truly is always something. Tomorrow I will see just what I've learned from this forum. Too late to take shell off tonight. My newly purchased Black Jack K-Line GG1 has been running beautifully. Tonight, all of a sudden, no TMCC response. With switch in "run," it goes forward when power applied. When switch in "program," it moves forward when power applied. All other locomotives work fine, so I doubt it is Command Base problem. No response to horn or whistle.
My guess: antenna wire broke or loosened? After a night's sleep, I'll see what I can find inside.
Interesting, though, that it only runs forward. I moved it to the "non-TMCC" track with a Powermaster, and it behaves there just like a conventional engine, but no reversing. Well, tomorrow is another day.