Lionel produced several 35- and 45-watt transformers through the years, including the 1010, 1025, 1015, and 1016. Lionel MPC produced a similar 4045 transformer in the 1970s. They’re small, but they only cost around $10 when you can find them, and can be useful when you string them together with other transformers. The problem is the markings don’t tell you what you need to know in order to do that. But I’ll tell you.

Lionel 1025 transformer pinout

Lionel 1025 transformer

On small Lionel transformers, the common post is on the right. This one goes to the outer rail of the track, and if you phase it with a larger transformer, to the common or base post of your larger transformer. The post on the right doubles as a direction control button.

Lionel 1025 and similar transformers have two posts, or terminals. The post on the right (with the handle facing you) doubles as the direction control switch. That post is the common post, or the base post in American Flyer terminology. When you want to phase a 1010/1015/1016/1025/4045 with another transformer, connect that right-hand post to the common or base post on your other transformer. Lionel didn’t label that post as such, but I recommend you do. The post on the left connects to the wiper, which is how you can determine the hot post on an unmarked transformer.

When wiring these transformers to the track, the post on the left is the one that will go to the center rail. Since these transformers lack a whistle control the train doesn’t care which post goes to which rail, but if you are trying to use it in phase with another transformer, the other transformer will.

Let’s talk wattage and amperage

The 35-watt versions of these transformers output 2.3 amps, while the 45-watt versions output 2.6 amps. These transformers and are fine for running switches and motorized accessories of course, and have enough amperage for a freight train, which will only have a headlight and perhaps a lighted caboose. But they may struggle with a lighted passenger train. The other place you run into problems with amperage is on larger layouts with track that isn’t pristine. A high-amperage transformer will get less voltage drop over that distance than a smaller one.

There’s no harm using this transformer in conjunction with another one while you wait for a good deal on a larger transformer.