If it is a typical starter solenoid, one small terminal is labeled "S" for "START" (goes to the start switch) and the other is labeled "I" or "R" ("Ignition" or "Ignition Resistor") and it becomes "live" while the solenoid is engaged to bypass the ballast resistor for a hotter spark during cranking.
You didn't say if it's a gasser or a diesel and if it's a gasser I don't know if a ballast resistor is used.
Bottom line if a diesel or a gasser without a ballast resistor you can IGNORE the second terminal.
The other scenario is that is is a special solenoid with both ends of the coil brought out to the two terminals. THAT makes things more complicated depending upon how the tractor is wired (safety switches, if any).
Where did you get the solenoid? Part #?