My first thought is that you are not making connection from the gound terminal of your Legacy Command Base to the outer rail(s) of your layout. To test, I would make a temporary connection from the Command Base ground terminal directly to the outer rail of the loop your engine is on, power on Legacy Base first, then the engine. If this works, then you need to figure out how you are missing the ground connection from Command Base to track outer rail.
As a minor second thought, Lionel recommended (at least they used to) that the Legacy Command Base be plugged to the wall without going through a Surge Protection outlet strip, as the Surge Protection Circuitry could greatly decrease the Command signal going from the Command Base to the earth ground of your house.
