rarely does adding a 12v battery kill it.
in any case.
polarize the genny ( jump bat hot to armature ) and then see what she does.
use a volt meter.. remember .. an ammeter can read backwards if you have changed the ground polarity.
a good test is to see if the needle deflects negative with ign on, points closed.. or lamp on, both with tractor not running.
if metr shows negative deflection on those.. then it is liekly wired correct with respect to ground polarity.
now.. if o charge after polarization do this:
slip belt off machine.. jump bat to armature.. ground field.
genny should spin. if not it needs a trip to the DR
if it does spin.. then it should charge. most gens that motor, will charge. most gens that charge.. will motor.
next.. assuming it motored..
slip belt back on.. start up tractor.. nothing on meter?
jumper field to ground.. if she starts charging.. but dies again when you remove jumper.. ensure wire harness from vrg to genny is intact. if it is.. vreg field circuit is bad... repalce vreg.
if still no charge.. then jumper bat to arm as well as leaving field jumped to ground.
if this produces charge, then cutout relay is open and field may be open as well in vreg.. etc.
post back observations..