As Sergio mentioned, without the steering diodes you'd have both coils of the reversing contactor energized and the half speed reverse activated at the same time with either F or R selected on the F/R switch.
Also looks like Alltrax needs to go back to the drawing board. They have a nonexistent switch in the main solenoid activation circuit. The "run-switch" between keyswitch and fuse does not exist if the original F/R assemble that the reversing contactor replaces was removed.
Personally, I would wire the new On-Off-On switch in after the foot switch and eliminate the need of steering diodes.
