@stan2004 posted:Right. This is one of those ask me how I know.
In some MTH operating cars, power can be provided using the normal truck roller-wheels (i.e., center-outer rails)...OR by the 4th/5th rails of the UCS. Of course the 4th/5th rails are only active when the UNLOAD button is pressed. The UNLOAD is a double-pole switch that applies track power to the 4th and 5th rails. The rub is an operating car can be facing either direction on the UCS. So it's a coin toss as to whether the 4th rail sliding shoe receives hot or common. Hence you cannot pre-wire one side and use only a single-pole switch (relay) to apply AC such cars.
I know the FET version will work on the MTH operating boxcars. It remains to be seen if the caboose's conventional bell DC offset detector (which the boxcar does not have) precludes a simple 3-wire connection of the FET version.
You're rewiring the car, just remove the UCS wires and just switch the center rail power. For a bell DC offset detector I have a solution.
Add in the string of diodes just like a whistle/bell button and use the remote to short most of the diodes in one direction. This exactly simulates what the transformer bell button would be doing and should solve the problem. I'm assuming you're running in command in this scenario since you'd have the actual bell button if you're running in conventional.
