Isolate the 'E' unit by removing all of its wires to the motor. Wire up the motor according to the diagram ''Wiring Diagram of Locomotives With No Reversing Mechanism''
The motor should run in one direction. Reverse the wires to the brushes and the motor should run in the opposite direction.
If the motor runs properly this way, the 'E' unit is faulty and needs servicing. It usually needs the drum and contact fingers replaced for a reliable repair.
Larry