The shop manuals have great wiring diagrams and details on how the glow plug circuit works. If you plan on doing much work, I suggest you purchase one. If possible, consider one of the vendors who support this site.
Sorry but I have a 855D, so likely not the same.
2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, 2500lb Winch installed in cargo bed, Front and Rear LED auxiliary lighting (4" square 27 watt), Front and Rear CV Guards, Koplin Side Mirrors