Are you powering the legacy base and the layout at the same time?
Its recommended that the base be powered first so it can get the signal to the track so the engines don't drop into conventional. Given the massive size of your layout I'd probably power the base up and wait a few seconds to power the track.
Is there some a loco or something "bridging" power from another block? The base shouldn't have anything to do with power to the track.
I'm confused about the power question? If your putting power to the track most TMCC/legacy locos will have lights that come on.
Only the most recent legacy offerings actually stay completely dark until addressed.