@TheLloyd posted:...thank you for digging into this...
Just to be very clear, neither of those red or green windings should be grounded at all. One set of field winding leads, a red & a green, is properly connected to the one brush... so that means that each other end, one red & one green, must go straight to the reverse unit. The other brush must be grounded to chassis.
All the reverse unit does is select which field winding, red or green, is connected in series with the brushes. The brown wire is the common return to the reverse unit and usually wouldn't be needed, but the reverse unit must need it for feedback. It looks like, based on some messy soldering, that some wires have been switched around.
