Last Updated on April 23, 2017 by Dave Farquhar
The Marx 1590 is the best O27 switch ever made. It’s durable, works well with all makes of trains (just put a track pin in the center rail where the switch pivots so that Lionel trains can pass), and can run off accessory power without modification.
The only downside is that it (allegedly) can’t be set to automatically switch to a position to accommodate an approaching train like a Lionel 1122, which makes it unusable in a reverse loop. That’s true if you wire them the way Marx said to wire them.
Here’s how I wire them to get that coveted feature.
First, refer to the diagram on the right to see where to put the track pins so that Lionel trains can pass through them. Place an O27 track pin where each arrow points to close the gap. With this simple, cheap modification, Lionel O27 trains and other makes of trains that use rollers instead of a pickup shoe run just fine on the Marx switch.
Run a wire from the center post on the Marx switch to the hot accessory post on your transformer (which may be labeled B or C). If you use a separate, phased transformer for accessories, use the A terminal on that transformer. If you want to run it off track power, which I don’t recommend, connect it to the A terminal of your train transformer. If you’re not sure which accessory post is common and which one is hot, this chart may help. Otherwise just hook it up and switch terminals if it doesn’t work.
Next, connect an insulated track section (which you can buy or make) to the curved leg of the switch and another to the straight leg of the switch. Connect a wire to the insulated rail of the insulated section connected to the curved leg, and connect the other end of the wire to the post closest to the curved leg. Next, connect a wire to the insulated rail of the insulated section connected to the straight leg, and connect the other end of the wire to the empty post.
Now when you run a train on the layout, the switch will sense an oncoming train and automatically switch for it.
If you want to use the Marx control panel to switch the switches yourself as well, connect your common wire (use the U post of your transformer) to the left terminal labeled “To Transformer.” Leave the other terminal empty. Connect the red terminal on the control panel to the terminal on the switch that corresponds to the curved leg. Connect the green terminal on the control panel to the terminal that corresponds to the straight leg. Leave the black terminal disconnected.
This modification to the wiring is all it takes, and when you run them off accessory power on the transformer, they are very responsive, even if you run your trains slow.
The Marx 1590 is everything the Lionel 1121 isn’t. It’s cheap and easy to find. With the addition of track pins in the center rails, it works with any train that a Lionel 1121 does. It works with Marx and early American Flyer trains, and it runs off accessory power without any modifications. What more could you want?
Wide radius, you say? Well, the very same wiring trick works on the wide-radius Marx O34 switch too. So there you go.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.