I've been asked not to bark.. but I'll start my message with a non barked, but important warning.
The 2nd fastest way i know to damge a charge system is to unload it by pulling a wire off the charge device or battery / load.
it lets voltage go sky high! There are actually different things that happen vs genny and reg and alternator.. however in general.. it's pretty abusive to the system... likle choking a gasser down every day to shut it off.
now that that's been said.. some observations.
1, sounds like a 6v electrical system.
Also sounds like you ?may? have it wired backwards... if it is not positive ground.
positive is ground, negative is the usual hot terminal.
You mentioned puiing the positive off.. can i then assume you meant you pulled the positive bat cable off? thereby disconnecting tractor chassis from battery ground.. something that should really never be done, anyway, during testing.
now.. if it did die, sounds like generaor was not making charge, unless this was at idle, in which case, most gennies won't generate power well at idle.
what does the center 0 ammeter show? charge or discharge?
is the ammeter wired correctly? with engine off and key on, points closed, does it show a 3-4 a discharge.. and a higher discharge when lamps are on? if not, ammeter is wired wrong or not working.
need to have a proper electrical system with working center 0 ammeter to mre esilly diagnose genny / regulator issues.
genny. motor test her.
strip belt off... jump bat hot to armature, and ground field.. genny should spin. if she does, she should charge. only very rarely will you get a genny that motors but does not charge ( generaly is a flaw in the field coil when this happens ).
if it motors, then belt back up and do a voltage test pre start. good battery is 6.3v nominal. after startup, at 2/3 throttle, ammeter should show some positive charge. also votlage on bat should be in the neighborhood of 7.2 to 7.3v ( 7-8 ) is more or less fine.
If lower than that, jump genny field to ground... if voltage comes up, check field wire from reg to genny with a jumper. it's either a bad wire or bad vreg field circuit.
if still no charge, leave field grounded, and then jumper bat to arm. if voltage comes up, you have a bad cutout and possibly field control circuit. ( replace reg if it fails either test and it's not just a wire between genny and vreg ) do test for both using umper wires before replacing a 40$ vreg.
post back if you need more instructons.