The KW is a well-known transformer, very versatile and powerful with its fixed and variable power connections. Given the age of most KW transformers, however, there are a few things that can need repair. The first is to be sure the line cord and circuit breaker are in good condition. The contact rollers for the two variable voltage taps are another thing to check, but the same replacement parts can be used for both Lionel KW and ZW transformers.
Remove the screws that secure the KW transformer case using a screwdriver,
Remove the transformer handles. Use a screwdriver to lift up each handle; they both lift off with a mild rocking effort.
Lift the KW transformer case off the base once the handles are removed.
Heat the soldering iron. When it's hot, touch it to each soldered ends of the power cord. Once both ends are freed from the base, discard the old power cord.
Tin bare ends of the new power cord with rosin-core solder. Then touch them one at a time to the solder joints, and add a drop of solder using the soldering iron to secure the new power cord wires to the transformer base.
Replace the transformer cover, re-attach the handles, and tighten the screws that hold the base.
25-watt pencil solder irons can be purchased for approximately five dollars.