The lock-on uses a modular 3 pin connector (only 2 pins wired) to bring in power from transformer or brick.
The U wire from the TMCC/Legacy base lands on a dedicated squeeze/spring connector in the lock-on.
The track terminal section connects the center rail to the A screw terminal and outside rail to the U terminal screw.
This configuration ensures TMCC/Legacy to the rails regardless of whether the lock-on circuit breaker is closed or tripped.