Electric model trains get their power supply from the track they run on. This means their wheels, the only parts touching the track, must be kept clean and clear of dirt and dust for the train to work properly. Dirty wheels often cause power failures in running trains and the first sign that something is up is a stall-out on the track or the engine's headlight dimming.
Dampen a paper towel with rubbing alcohol.
Lay the paper towel on the track with the dampened parts over the rails.
Tuck the towel down so that no part of it can be snagged on the underside parts of the train, such as the coupler pins, says Jim Volhard in his book, "Maintaining and Repairing Your Scale Model Trains."
Allow the car to run over the paper towel. Pick it up off the towel once it is no longer over the damp part. Repeat this a few times, moving the towel slightly so that the wheels are always contacting fresh alcohol.
You may also use a cotton T-shirt or cloth, and stretch it tightly over the rails. Do one car at a time, rather than allowing the whole train to run over the cleaner. It will clean the wheels more effectively.
Only barely dampen your cleaning cloth when dealing with electric trains. Excessive moisture can cause shorts and even electrical shock.