I have the same on my FX28D. Don't know what they do, but probably adjust the set point of the joystick control (which on my tractor ocasionally goes crazy). Disconnect everything (unless you are planning to be a rice farmer).
Branson 4520r 5520C- Yanmar FX235-D - Bad Boy rogue mower
Cfox,
They are knobs for the automatic tilting of the 3 point when you have the correct tiller on the tractor.
Thats what mine does
Ernie www.ernies.net