The "box" behind the light is the reverse unit. TO check if the E-unit solenoid is getting power. Put it on the track (or attach alligator clips) and cycle transformer power from off to on - minimum voltage. You should be able to hear the solenoid engage on each application of power. Note: the E-unit only cycles with the motor right side up.
If it's not moving it could need some service. But first check the E-unit's power switch. A little lever on the side of the unit. When engaged, the E-unit's coil gets power from the center rail and cycles with track power.
The level can be moved to break that connection. Thus the solenoid never gets power and the motor remains in it's last direction.