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There are three parts to a simple reverse section when controlled with an ARSC: two detection portals, and the reverse section itself, as shown at right.

While the reverse section is always powered with one polarity or the other, only one portal is powered at a time - the other portal is in the detection mode.

When a loco enters the north portal, from either direction, polarity in the reverse section is set to match that end, the north portal is powered, and the south portal goes into the detection mode.

When a loco enters the south portal, from either direction, polarity in the reverse section is set to match that end, the south portal is powered, and the north portal goes into the detection mode.

If the loco is within the reverse section when this happens, polarity is switched right under the loco. But, because the decoder is controlling which direction the loco is going, regardless of polarity, the loco doesn't react to this and just keeps going in the same direction.

The requirement for the ARSC to know a loco is present is that two powered wheels must be in the detection portal at the same time at least two powered wheels are outside the portal. With all-wheel power pickup locos, this always happens. With most lighted passenger cars, this doesn't happen because they pickup right rail power from the front truck and left rail power from the rear truck. This is how the ARSC tells a loco from a lighted passenger, or other power pickup, car.

Most older steam locos only pick up right track power from the right drivers and get left track power from the left tender wheels - making it look exactly like a lighted passenger car. This is why power pickup has to be added to these units to make the ARSC work.

While the loco doesn't have to have all-wheel power pickup, it does have to have power pickup on both wheels of the first axle that has power pickup. And if you want to be able to back through the reverse section, it also must also have power pickup on both wheels of the last axle that has power pickup.

You should add power pickup to all-wheels just to have a better running loco. It's fairly easy with Tomar's all-wheel power pickup kit. If you want to see how it's done, check the article about it on page 112 in the March 1995 issue of Model Railroader. The Tomar kit provides all the parts you need to do this installation.