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AF Steam Engine Tester by Ben Swope

May 7th, 2015 · No Comments

Many American Flyer S Gauge hobbyists enjoy restoring their vintage equipment. For me, restoring these old worn items back into their original operating condition has always been one of my favorite parts of the hobby. Let’s look at a homemade tool used to assist servicing American Flyer steam engines, and how with a little effort and a few simple parts, you can construct your own.

Several drawings, both in-print and on-line, have shown the standard 4-wire connection of AF steam engine’s rear of cab electrical jack panel; where to place a jumper wire on the panel, and where to apply the power leads when the engine is not connected to the tender and its reversing “E-unit”.

One on-line resource Port Lines displays some very nice wire schematics of the standard 4-wire and the 5-wire engine/tender connections, along with the other 2-wire type tender connections; each noting the jack panel wire locations leading to the various connections on the engine drive motor, smoke and headlight connections, and the tender and reverser wire connection points.

After a search for information on how to create a four or five-wire steam engine test wire harness; one that attached directly to the engine’s jack panel, none could be found. So I created on my own.


Ben’s Test Wire Harness for American Flyer Steam Engines

The accompanying drawings show first, a 4-wire test lead utilizing a simple double-pole-double-throw (DPDT), center-off toggle switch to create a forward/off/reverse option.

Switch “A”: The motor direction switch, being a double-pole double-throw, center-off switch. This switch performs the same function as the tender mounted reverser.

The next drawing adds a second DPDT switch to the circuit, making it switchable from a four to five-wire engine/tender wiring design. An optional on/off switch may be used to make a connection to the smoke unit and headlight for engines with the 5th tender wire connection.

Switch “A”: The motor direction switch, being a double-pole double-throw, center-off switch. This switch performs the same function as the tender mounted reverser.

Switch “B”: Also a double-pole double-throw; used to compensate for the difference in the 4-wire to 5-wire connections to the motor brushes/field coil.

Switch “C”: Optional single-pole on/off switch; connecting the smoke unit/headlight to the power source through the direction switch.

The four wires to the jack panel were soldered to a salvaged male plug off an unused tender chassis.

The 5th wire for the smoke/headlight connection may be connected to the engine by using a small covered alligator clip or similar device. On my engines, this 5th wire connection typically is converted from a factory soldered connection to a homemade 1/16-inch jack plug and socket using brass tubing; thus for servicing, the tender can be easily and totally disconnected from the steam engine.

This wire harness assembly will allow you to leave the test leads attached during servicing work. And it comes in handy when the engine is turned upside down, as an attached tender’s reverser will not work in this inverted position.

In all, this is a rather simple electrical circuit (if I can figure it out – it’s got to be simple), with all of the components coming out of my parts box. I used colored wire, but any color of flexible light-gauge stranded wire would work. I found the color and polarity of the two power lead wires doesn’t matter if you’re using AC current.

To keep things neat and flexible in use, I braded the wires from the switches to the male plug, and slipped on a bit of heat-shrink tubing before soldering the final wires into place, but tape could do the same. The toggle switches used were of the tiny sub-miniature type. These toggle switches were small enough to mount all three into an old style empty AF control box; and would be handy if you wanted to mount the control box to your workbench.

This harness, by isolating the tender from the engine, may aid in diagnosing an electrical problem. For example, if the engine runs fine on the harness, and not when connected to the tender, obviously the tender has an issue.

Also, do not attempt to operate a 4-wire engine on the 5-wire switch setting (or visa-versa), as the resulting electrical short may damage the engine or power source. Labeling your switches will help avoid this situation.

The bit of work to assemble this test wire harness assembly may save time and hassle on your next steam engine service work. And best of all, it cost just a few dollars to make.

Ben Swope

Tags: Main Line

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