I only have one 3/2 steam engine. PS&N Russian decapod. Just some information about how it is assemble to achieve the 3/2 configuration. Keep in mind three rail allows for common from both outside rails.
Locomotive is split down the middle each left wheel is electrically isolated from the right wheel including the pilot. All left wheels are common and show continuity through to the frame. All right wheels are isolated. 
The tender is designed for two rail pickup with the (4) axles as pickup. (2) Axles, front truck, are power right rail. The front axles are isolated from the frame with plastic inserts in both side frames. The (2) axles, rear truck, are common left rail with the right wheels isolated. One of the truck side frames has brass inserts for the axle. Common pick-up through the truck frame and the frame of the tender.
Three rail pick-up center rail is via the two installed third rail pick ups. A wiper assembly was add to the front tender truck to increase outside rail pickup via the other rail. A couple of pictures.
Rear tender truck notice the brass inserts in the truck side frame. the wheels, bottom of the picture, are isolated from the axle. Common pick-up (left) (Two rail).
The front tender truck is designed, (two rail), for pick up of power on the (right) rail. The isolated wipers are added to allow for Common pick-up via the (right) rail when the third rail pick-ups are added. Therefore you have Common from either the left or right outside rail.
Noted difference front truck is the axle wipers and the plastic axle bearings.
Plastic axle bearings are both sides isolating the axle from the truck frame.
Remove the thirdrail pick-ups, leave the wiper, switch the three/two rail switch and it should be ready for two rail operation.
The wiper assembly on this axle appears to allow for common pick-up from both outside rails when the third rail pick-ups are added. Tender switch in the three rail position.
The Tender if all wheel/axles are assembled properly with the wipers should allow for common pick-up off both outside rails. Locomotive only allows for one side common rail pick-up.
Susan should check the tender for the brass insert bearings that allows for the two outside rail pick-up as it moves through a switch. If all axles are have plastic bearings the only outside rail pick-up is via the wipers shown. Limited outside rail pick-up as she indicated. I could be wrong and often.
Best wishes with your project.
Mike.
