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Re: 12 v positive or negative ground

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Author  [Modern View]

03-24-2013 09:03:29

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I've been following this discussion, and piecing things together it appears that

The tractor in question is a Massey Ferguson 35. Diagram at FENA dot org / resources / wiring diagrams / MF35 shows it is 12 volt, negative ground and regulator shows Type A circuit (field of generator to grounds through regulator.

The notes in question are for a 650 Ford which would be a type B charging circuit.

Looking at the notes:
"1. Using volt meter momentarily jump the ARM and BAT terminals. Charge should be about 7.8. If not, then replace the regulator.

2. Jump the ARM and FLD terminals. If there is a charge, then replace the regulator. "

Let's apply some life experience to note taking and understand that notes are often quickly written and later confusing to read.

With that in mind lets interpret note as probably intended: 1:Using volt meter (CONNECTED ACROSS THE BATTERY) momentarily jump the ARM and BAT terminals. Charge should be about 7.8. If not, then replace the regulator. This bypasses the cutout section of the regulator and would make sense.

Note 2. Jump the ARM and FLD terminals. If there is a charge, then replace the regulator. " applies full field to a TYPE B SYSTEM and tests the regulator side of the regulator box.

If applied to MF35 (Type A) it should be GROUND THE FIELD TERMINAL

Attached diagram shows difference between Type A and Type B.

A generator system, if properly configured can operate either positive or negative ground

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03-24-2013 10:19:34

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 Re: 12 v positive or negative ground in reply to rvirgil_KS, 03-24-2013 09:03:29  
Thanks, rvirgil. Thanks especially for the link to the wiring diagram on the MF 35 - showing NEGATIVE ground. Interesting, indeed.

(Everyone else ignore this paragraph so as not to confuse anyone). Brother has a MF35 manual on a CD for his tractor. He printed out wiring diagram. He and I looked at the diagram. His concern, then later mine, was that his diagram showed POSITIVE ground, while the tractor battery is installed NEGATIVE ground.

(I shall visit with him and learn the source of his CD manual.)

In any event, rvirgil, the link you provided reflects negative ground and his tractor is negative ground. Thus, will assume that electrical system worked fine as configured until the voltage regulator went bad - from whatever cause. Since generator has been rebuilt by "outside shop", is clean-grounded, wiring replaced to VR and new VR on the way - I feel much better about replacing the VR without fear of "destroying" it or the generator.

Very helpful!

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