American flyer #3020 prewar 4-4-4 wiring or mechanical schematic

American Flyer #3020 Prewar 4-4-4  Does anyone have a wiring schematic of this engine  or  a breakdown of the reversing unit  This reversing unit does not have contact fingers or drum like most O & S gauge AF locos My book only describes it as a late #3020 have a 2pc reverse unit with square rods  I can get it to run by bypassing the rev unit. So I know the problem is in the rev. unit Thanks for any help