How to replace a Lionel transformer power cord

Last Updated on September 2, 2017 by Dave Farquhar

When using vintage Lionel transformers, it’s important to make sure the power cord isn’t broken or frayed to avoid the risk of electric shock or starting a fire. If yours is, here’s how to replace a Lionel transformer power cord.

Replacing a power cord safely is a lot easier than most people make it sound. It’s possible to do the job safely with simple tools and a few dollars’ worth of parts from the nearest hardware store.

I’m going to talk very broadly and generally here. Some Lionel transformers disassemble differently from others; I’ll follow up as I have time with specific instructions for various transformers.

You are working with electricity, so you’ll need to follow safety precautions. With the help of a knowledgeable friend, you can do this. A friend who knows how to safely and properly replace an electrical outlet and get the polarity correct is qualified to help you safely change a plug on a Lionel transformer. If you can do that task yourself, you can manage this too.

What you need

You’ll need a screwdriver, wire cutters, wire strippers, a heat gun or a household hair dryer, two wire nuts (yellow is the largest acceptable; the smaller orange, blue, and tan nuts will also work), about two pieces of small shrink tubing and a couple of larger pieces (buy an assortment pack), and a power cord. You can buy an inexpensive extension cord and cut off the end, reuse a power cord from a discarded small appliance, or buy a new replacement cord.

Getting started

First, and most importantly, unplug the transformer. You shouldn’t plug in a bad cord anyway, but I have to say it. This is critical. There is no voltage whatsoever in a Lionel transformer if it is unplugged. But only if it is unplugged.

Next, open the transformer. Usually there are four screws holding it together. There may be handles on the top as well; handles usually lift straight up to remove. Every once in a while, the handles themselves have a screw on them as well. Set all parts aside for later.

Usually the case lifts straight up once the screws and handles are free.

The cord is soldered to the transformer core, sometimes in a way that requires you to completely disassemble the transformer in order to reach it. We’ll work around that.

Prepping the transformer

Cut the plug off the end of the old power cord, then thread the wire through the opening in the transformer case. Untie the knot in the wire inside the case, and cut the old wire off near where the knot had been, leaving enough room that you can strip back a good inch or so of wire from the old cord.

If the old cord is frayed inside the case, separate the wires if they’re still attached to each other. Then slip a piece of the heat shrink tubing over each wire. Use piece that’s more than large enough to cover any bare copper that might be showing.

There may be one or two layers of insulation to what’s left of the power cord. Strip back about a half inch of the black insulation at first. If there’s a second layer of insulation, strip back another half inch or so of the black insulation, then strip back a half inch of the second layer. In the end, you’ll want about a half inch of  bare stranded copper showing. Take each piece of wire, one at a time, and twist the strands together so they look like a braid.

Prepping the cord

Do the same for whatever you use for the replacement power cord, assuming it didn’t already come that way, then thread the bare end of the cord into the transformer case, the same way the old cord was, and tie a knot in the cord the same way the old one was. Position the knot so that if you tug on the power cord, there’s still some slack in the case so you can’t pull the wire apart.

The polarity of the transformer is important if you have more than one transformer. One of the wires on the old cord may be ribbed, striped, or white. On your new cord, look for a wire with ribs, a stripe, or white insulation. You’ll want to match these two wires together. If both wires on the old cord are the same, don’t worry about this.

You don’t need to know how to solder in order to continue, but if you do, you have a second option as far as connecting the wires.

Replacing the cord — the soldering method

At this point, if you know how to solder, or are willing to learn, you can solder your wires together. If you do this, you won’t need a wire nut. Slip a piece of shrink tubing onto one of the wires. Pick up the wire and its mate, twist the bare copper together, then solder it. Let it cool. Fold the soldered connection over the rest of the wire. Then slide the piece of shrink tubing over the connection and shrink it with a hair dryer. This adds strength and insulates the connection. Make sure you didn’t accidentally twist two ends from the same cord together–this creates an unsafe electrical short. You’ll make two pairs, each one old to new.

Repeat for the second wire pair.

Replacing a Lionel transformer power cord without soldering

If you don’t want to solder, pick up one piece of wire from the new cord and its mate from inside the transformer. Twist the two bare copper ends together. Then twist a wire nut clockwise onto the connection. If the nut isn’t big enough to cover all of the bare wire, untwist the nut. Trim off enough of the slack so that the nut will fit, then twist the nut back on.

Take a piece of shrink tubing and slide it over the end of the wire nut. Position it so that part of it is sitting on the nut and at least half of it is sitting on the insulated pieces of wire. Then shrink the tube down with the heat gun or hair dryer. This ensures a firm, safe connection.

Repeat the process for the second wire pair.

Reassemble the transformer by reversing the disassembly process.

Testing the transformer

When you plug the transformer in, it will hum slightly. You’ll be able to measure a few volts (anywhere from 12-18) off the accessory terminals with a voltmeter. You’ll also measure a variable amount of voltage off the track terminals when you turn the handle.

If you don’t have a voltmeter, you can test it by connecting small lengths of wire to a the track terminals. Then touch one end of the wire to the pickup on the underside of the train and one end of the other wire to the wheels. If the transformer is working properly, the train will light up, the reversing unit will cycle, and either the wheels will turn or the train will go into neutral. Pull one wire away and touch it again to kick the train out of neutral. If the train is lifeless, the transformer has other problems or the cord wasn’t wired properly. Immediately unplug it and double-check your wiring at that point.

If you use more than one transformer, here are my instructions for how to phase them so you can use them together. If the polarized plug keeps you from being able to phase them properly, you can fix that. File down the thicker prong so that it is the same size as the other prong. Then you’ll be able to rotate the plug and phase the transformers properly. Be sure to mark on both plugs which way is up.

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