Farmall A not charging

wok42 · Jul 11, 2017

Farmall A 6V generator not charging. Generator is good as it charges when field jumper wired to ground. I don"t get continuity from the switch"s field terminal to the box cover or the switch"s casting. Shouldn"t that happen and switch bad?

teddy52food · Jul 11, 2017

It has to complete the ground to make the generator charge.

Janicholson · Jul 11, 2017

Tracing a ground is a little backwards but useful. Put one test light (or volt meter lead)on the non grounded battery terminal. use the other lead to assess grounding of the chassis, battery box, electrical box, and switch body. if any one of them fail to light the light, clean (or jumper with a ground strap) to make a circuit. If the switch housing is grounded, but the field lead terminal doesn't show about 2-3 ohms, or no resistance to ground, the switch is bad. You can measure the contenuity of the resistor (out of the circuit on one end) they can become open. Make sure your wires are connected to the generator control portion of the light switch, and not the light circuit. Both have resistors. Pictures of the switch are found on line. Jim

gene bender · Jul 12, 2017

Rule of thumb is when the gens field is ground the reg is the culprit and when the field is grounded and it dont charge the gen is bad. But it sure wont hurt to check groud on all componets. Lots of times the sw box is also needs to be removed and then cleas the area where it fastens to the post. I use an OHM meter with one lead connected to batt ground and then other probe to all componets to check for a good ground.

John T · Jul 12, 2017

wok, Good advice below, FWIW I agree and here's my take, you pretty well answered your own question

"I don"t get continuity from the switch"s field terminal to the box cover or the switch"s casting. Shouldn"t that happen and switch bad?

YES there should be continuity (near 0 ohms in HIGH charge, maybe 2 to 4 ohms in LOW charge) from the switches field
terminal to the tractors (and eventually to the grounded battery post) frame ground.

YES switch could be bad

YES there should be a good wire near 0 ohms of resistance from FLD on the Genny up to the switches field terminal

More often then a bad switch, I find the problem to be the switch isn't well grounded. Try a grounding jumper wire from switch to a good clean shiny metal ground.

Indeed if it charges with the gennys FLD grounded but NOT otherwise, the genny isn't getting a good ground via the switch via its resistor (in low charge) via the switches frame ground connection.

John T

wok42 · Jul 14, 2017

Thanks -- I found the grounding problem -- switch to box cover. -- wok

Farmall A not charging

wok42

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teddy52food

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gene bender

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John T

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wok42

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