Battery Drain

1941 Farmall A.
Just did some painting, including the electrical box. Things were great before the paint job. Upon reassembly, turning the knob past the "home" position of "L," I get the ammeter pinned suddenly to minus 17...all the way pinned to negative. My battery has discharged to the point of not being able to operate the starter. Did I lose my ground somehow with paint somewhere? Had to solder a connection that came loose from the crimp, but otherwise connected everything up correctly, tightly and even brightened up some lock washers and other mating metal parts. Electrically compromised Tom

Hmmmm. Sounds like a dead short so I don't think you lost a ground, I think you gained one. Your switch does ground through the panel/box/steering support, and it needs the ground for the charging circuit. If you'd lost the ground with paint (it happens, as you are obviously aware) you should lose the path to ground for your charge which would show a little discharge with a load, but nothing like pegging out at the bottom. Best idea I can offer at this stage is to trace everything in and out of the box keeping an eye for anything that may have gotten cut or pinched. You've developed a short somewhere.

I don,t think you lost ground.It would appear you may have created a short circuit.Disconnect- cable and RECHARGE BATTERY.using a two wire buzzer or bell same voltage as battery,connect one wire to vacant bat.post & 2nd wire to loose cable.If there is a short,buzzer will sound.Duplicate knob position that caused problem,buzzer should sound.While buzzer sounds,move,wiggle, disconnect until buzzer stops.THERE IS THE PROBLEM.

The soldering may have allowed some conductor to touch the electrical box metal. There are no internal grounds in the box at all. The light switch is a ground through its field control circuit. (all positions of the switch go to ground the field circuit. (see the diagram)
The switch has a light control circuit that is seperate from the grounding ofthe field.
When in L the field is grounded through a wire wound resistor (which may be toast now) The field is in Low charge when in the L position.
All other positions are high charge.
If you accidently wired a light supply wire to the Field terminal, it would give those symptoms, and burn the resistor. Let us know, and good luck. JimN

Here are the best. JimN
Bob M diagrams of high value

Morning, Jim!

Now I'm confused. Nothing new there, really. And I'm only on my second cup of coffee.

But stuck in the back of my alleged mind is a thread from a few months back where the problem was a fellow losing the ground contact between the switch body and the frame of the tractor. Can't recall what his symptoms were, though, that led us to that solution.

My thinking below was that the lights find ground through their housings, the only choice being whether the current through the switch passed through the light resistor or not.

From that point, I assumed that the problem I referenced had to do with the function of the charging resistor. I don't have a switch laying around just now to open up and go through, but a quick look at a wiring diagram in the parts book doesn't show any direct wire ground connection on the charging circuit. The wire from the field terminal stud on the generator runs to the switch by way of the ammeter.

You're my guru on this stuff, so I expect I'm missing something. How does the charge circuit get back to ground if not though the switch body? Is there a connection through the body of the relay?

Do you recall that older thread?

Clearing up mud (letting it settle)
The internals of the switch have two seperate parts, one is for charge control, the other is lights. They are on the same shaft, and in the same Molded plastic housing, but do not connect electrically.
The light sw part has a D and B function which takes its supply from a wire going to the Amp meter load side. The D position connects this power to a resistor (on the switch), then to the light wire out put. The B position connects the same input to the light wire directly, no resistor.

(I would have put two bulbs or filiments in the bulbs and had the D control one, and the B control the other, much brighter than normal lamp, but I was not born then nor working for IH)

The Field control is (for sure) not connected to the power at all. It is "ground only" (through the switch internal bushing and mount to the Electrical box). This is direct to groung all the time when the H D and B positions of the Switch knob are selected. When in the L position (full CCW), the Field is grounded through a wire wound resistor (also mounted on the Switch). This resistor cuts the field current to about 13 of full output. #4 on bobs diagrams. (If I remember) JimN
Bob diagrams