12 volt negative ground generator?

I recently acquired a allis wd-45, converted to 12 volt generator, negative ground, when I first got it last fall, charging system worked fine, now the push/pull light switch gets hot when the battery is hooked up, tractor not running. I take the front wire off of the voltage regulator, all is fine, except it will not charge the battery. when I hook up the battery cable I polarize the battery terminal on regulator and the field terminal with a quick touch with a jumper wire. can anyone tell me the reason 12 volt generators are usually positive ground and why alternators are negative ground? also, think if I reverse my wiring for the ammeter and the coil to set up for positive ground, my problem will go away?

IIRC, this would be a Delco "A" circuit generator.

If so, you do NOT polarize it by jumpering the field and battery terminals at the regulator, but rather the "BATT" and "GEN" (or "ARM") terminals.

At this point, at the very least, it sounds to me like the contacts in the "cutout relay" in the VR are welded/stuck.

NOT sure why the light switch is heating up, unless there"s other issues with the "FLD" circuit.

"tell me the reason 12 volt generators are usually positive ground"
There were LOTS of (-) ground 12 Volt generator systems.

"think if I reverse my wiring for the ammeter and the coil to set up for positive ground, my problem will go away?"
No.

polarize the way BOB says and it should work is your regulator made for Neg ground. You need the same polarizing as the reg says genny doesentcare

The only 2 reasons the light switch can get hot 1) if the Switch is internally shorted to ground
2) if the switch is broken internally and passing voltage to the light circuit, but with a poor internal path to the switch contacts. Replace the switch. (this assumes the switch was in the off position) If it was in the on position the switch is broken and not providing a clean connection to the light circuit, or the light circuit is shorted to ground, or the lights are wrong and drawing way too much.

If the system worked, and the amp meter showed charge when it was working, the reversing of the amp meter has already been done.

If the generator is a Delco "A" circuit type, (as noted) it is not polarized by touching the Field ever. Touching the field with battery voltage shorts the regulator field contacts and can weld them together, or other dammage.

If it was off of a Ford automobile or tractor It could be a "B" circuit system, and is polarized the way you did it. To find out which it is, put the part number into google with the brand and read what it is.

To correctly polarize an A circuit, the jump goes from Bat terminal to the Arm terminal.

Obtain a wiring diagram for the tractor, it will be tha same with either polarity with one exception. The Ignition coil should have the lead connected to the distributor's polarity match the battery ground. If negative ground, the Negative of the coil is connected to the distributor. Jim

Dad converted our JD-70 to 12 - ground with a generator from a Chevy car.