Lionel Prewar Wiring Diagrams - Classic Toy Trains Magazine

Here is the diagram for F-N-R "E" models - shows 2 lights but disregard that connection for 1 or 0 lights. Click on image for large format.

Some locomotives have the connections to the brushes switched with the connections to the field at the E-Unit(it doesn't matter - works the same) by grounding one brush instead of grounding one field wire.