Working on restoring a 474 engine. I'm more familiar with wiring Lionel Engines and E-Units. I've been using colored high lighters on the wiring diagram and still can't quite figure it out - diagram attached.
From my understanding, The Lionel E-Unit changes which rail goes to a specific brush and the other brush goes to the other rail. The coil is in series with the later line going from the brush to the rail.
From tracking the diagrams, the AF reverse unit changes whether the rear truck goes to one side of the coil, or the other. The flow through the brushes appears to be the same - sketch attached. If I have that right - I get how how power flows through the brushes, but the coil seems to leave one side open. I'm sure I am missing something.