Lionel’s e-unit is the most common cause of trouble in vintage Lionel trains. Sometimes people bypass them or remove them entirely to avoid dealing with the problem. Or maybe someone attempted a repair in the past and you just bought the remnants. If someone did that and now you want to replace or rewire it, you need a Lionel e-unit wiring diagram.
You found one.
A Lionel e-unit diagram and explanation
Most Lionel e-units follow the conventions in the diagram below.
The two yellow wires from the e-unit go to the motor brush holders. One wire usually reaches further than the other, so just attach them to whichever brushes they can reach. The e-unit usually has three more wires. One runs from the collector shoe or rollers to the e-unit coil. Another black wire runs from the coil to the headlight and/or the smoke unit. A third wire runs between the e-unit drum and the motor field. This wire may be black or green.
I covered how a Lionel e-unit works in a separate post if you’re curious. It can seem like black magic, but essentially it uses a solenoid to change the motor’s polarity.