Sometimes you may want to remove an e-unit from a Lionel locomotive and rewire it to run in forward only, whether as a temporary measure while you repair the e-unit, or as a permanent modification.
It only requires a few splices to get the job done.
First, disconnect the wire running from the motor’s field (the big wire coil that’s visible without disassembling the motor) from the e-unit. Disconnect the wire running from the headlight to the e-unit as well. You can desolder wires if you don’t mind soldering, or you can clip the existing wires and splice to them if you need more length. I have some soldering tips if your soldering skills could use a little help.
Next, disconnect the two yellow wires running from the e-unit to the motor brushes.
If you removed the wires to the brush holders, get two new wires (I recommend staying with yellow) and solder those to the brush holders where the old e-unit wires were. Connect the top yellow wire to the wire from the motor field. I recommend using a small blue wire nut, as this will make it easy to correct mistakes and/or undo the modification later. Connect the bottom yellow wire and the headlight wire to the pickup roller assembly using a blue wire nut. If any of this is unclear, refer to the schematic to the right.
If you find any of the wire insulation is missing, a cheap and easy way to shore it up is to slide a piece of 3/32 heat shrink tubing over it before making your wire connections.
Remove the e-unit if you wish. Since the going rate for a functioning Lionel e-unit is $30-$45, I assume if you’re bypassing it, you intend to remove it and use it in another engine.
Before reassembling the locomotive, test the motor to make sure it runs forward. If it doesn’t, swap the yellow wires. If the motor doesn’t run at all, you need to ground the other end of the motor field wire to the frame.
What about Marx trains? It’s very similar, but not quite identical.