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12 Volt Positive Ground

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YTSupport

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Anyone know what year AC switched to negative ground. Wiring diagrams for the early D15 showed 12 volt positive. D10/D12 manuals show 6 volt positive but I know that is wrong for the later ones (the three 61s I have 15, 17, and 12 appear to have been factory 12-volt positive ground).

I went to the warehouse to get some Electronic Ignitions for both the D14 and Kim's D10 and hadn't thought much about it until I remembered that hers is positive ground and that the EIs had to be matched to positive or negative. It's a 1964. In looking through my manuals, all the wiring diagrams through D-17 SIV show positive ground. I don't have a D-19 wiring diagram so couldn't look that up, but both D-21 manuals show negative ground.

My guess is the switch was made around 1965? Anyone know?
 
I remember working on dad's AC 170 which had a 12v positive ground alternator. Dad had bought an alternator tester which was advertised to test all alternators, but when I opened the box, it said negative systems only. So I returned it to the store.
 
If changing to electronic ignition, I would go by present ground configuration and not by what it shows in the manual.

The manuals may show the original factory configuration as positive ground. However, many tractors of all colors have been converted to negative ground over the years.

If properly configured they will run equally well with either ground polarity. I have all of mine converted to 12 volt, negative ground to make them compatable with and less confusing to people of the present times who are only familiar with negative ground.

Generators are quite forgiving of a momentary reversal of ground polarity. Alternators and electronic ignition modules are not.
 
Yes, my D14 is 12v negative (still running the 6v starter) and I've polarized other tractors to negative when it was time to put new cables on, but I was going to leave Kim's as original as possible (and I just rewired the battery connections with some very expensive battery cable and ends. It would probably reach to switch it over, but it's still positive ground).

The positive ground 12 volt EIs are way less common, we had only a single one in stock because no one ever buys them. But it set me to wondering about how long they continued to use positive ground. Cars must have all been switched by 1964 and the other post concerning the 170 suggests they were still positive even later than I thought. That would put it all the way up into the 70s. The One-Seventy still had a generator but negative ground on release in 67, but apparently the 170 was alternator positive ground. One-Eighty Negative ground. I'm starting to think they had a mixture for a time.

It's a minor point, I was just curious.
 
That's pretty interesting because the earlier One-Seventy started out with a generator and negative ground and I assumed they'd changed over by then. Don't have a manual on the 170 and have never owned one.
 
I can assure you all, that when A-C went to GM alternators, they were NEGATIVE ground. Now, I know of ONE D-17 tractor that when it was converted to a GM alternator (for a corn planter) the mechanic disassembled it and switched the diodes around to actually make it positive ground. He did this so keep the tractor original, he said. He was a genius in his mind. I'm not sure he was smart enough to switch the wires on the ammeter and the coil, but he knew how to reverse polarize the alternator !!!
 
Sounds like he was avoiding the effort to remove side panels and dash. I suppose the defense was shop time could be lower that way. I've never heard of doing that before, but I do nothing with alternators aside from black boxing in cars and trucks.
 
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