If the small wire from the switch to the solenoid is suspect a simple continuity test would quickly ID if the wire is ok or not.
Since you've tested a number of electrical components, I'll assume you're handy with a volt meter.
The workshop manual has good electrical schematics and theory of operation to better understand how everything works. Well worth it if you plan on doing your own repairs.
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