problems running Legacy

Lack of sufficient signal. Could be the U terminal of the Base output or could be some shielding of the air signal by overhead track etc. Hold your hand over the engine when the headlight is blinking and see if it comes on solid. Then it's the latter. If it is the lack of U output strength, your base may have gone bad as to the level of it's output or possibility dirty track or wheels. 

I have run Legacy since it came out.   One of the early things is the Command Base should be above the track.   On my last layout I had it lofted 3 feet above the track in one corner.  It does work better.   Another oldie  is have the command base power pack plugged in by itself and on a different house power line then the track supply.

Are they programmed to unique id numbers?  

did you check all of your track connections?

Bingo. I've had a Cab 1L for months now with the same symptoms as the OP. The base was pretty much under the train table with track and wires above it. Moved the base to table level this evening and problem solved. Thanks to those who responded with this solution.

when I hold my hand over the engine, the blinking stops.  how do I rectify this problem?

Was the base light not flashing when you made any hand held commands?

The blinking headlight issue is a different problem.

The third pin on the power cord or wall wart is the house ground. It carries the "other side" of the signal to the engines...the signal that the antenna in the engine receives. Raising the base up above the layout helping probably helps because the ground wire in the power cable to the base is up in the air now over the layout. You could probably accomplish the same results by connecting a wire to the ground (pin #5 on the DB9 connector or the ground pin on the power cord) and extending it along or over the layout. This would also be a solution for the symptom where your hand held over the engine helps.

there is another possible issue where the signal out of the U terminal is insufficient in amplitude. This has been reported by enough forum members that a way to measure it with a multimeter has been developed. Look here...

https://ogrforum.ogaugerr.com/t...gnal-strength?page=1

Thank you all for your insightful comments and recommendations.  I will start applying some of your advice, and will let you know what happens.

Stu