Positive / Negative Ground

My D17 has starting / electrical issues.

The tractor is wired negative ground, and, when it works, the tractor starts fine. To me this implies it must have been set to run negative ground, else the starter would spin the wrong way, yes?

I'd like to fix the wiring, but I'm not sure how things should be wired if it's negative ground. I also see a manifold heater mentioned in the wiring diagram in the I&T. Is that on all diesels, or was it an option?

Thanks in advance.



Edited by Coke - 02 Oct 2018 at 6:59pm

For the first several decades of electrical starters and electrical systems on tractors, trucks, and cars engineers and supervisors argued over polarity. Their experiences generally proved that either polarity worked so long as it was maintained, e.g. the battery connected properly and the generator flashed when the generator was replaced or was left setting a long time. Even when vacuum tube radios came along they were generally tolerant of either polarity if they used a vibrator and a rectifier. If they used a multiple pole vibrator to create AC and to rectify it as some two way radios did they were polarity sensitive but weren't destroyed if the polarity was reversed, just didn't work. Many used a special vibrator that could be rotated in its socket to change the polarity to solve that problem.

As transistor radios came along in the early 60s they were absolutely intolerant of reversed polarity because reversed polarity destroyed all the transistors in the radio. As a result, the SAE standard for vehicular electrical systems about 1963 specified that only negative ground was allowed. Deere ignored that for a few years but by about 1975 followed it. Long about that time the SAE standard also removed 6 volt systems and limited 24 volt systems.

The normal starter uses a single power connection and a series field so that reversing the power polarity doesn't change the rotation direction. Incandescent lamps are not polarity sensitive either. Fuel gauges can be power polarity sensitive, and ignition coils are polarity sensitive for sure as are battery monitoring ammeters. But for those reversed polarity isn't destructive, just the ammeter reads wrong and the reversed polarity ignition coil doesn't produce as great a spark.

Having equipment with mixed battery polarities was always confusing to users without some electrical training and jumping with the wrong polarity could destroy both machines because it essentially hooks both batteries in series and then shorts them.

Negative polarity as the universal standard since the 1960s removes that chance of confusion and is good for safety and there never was any evidence that otherwise the polarity of the electrical system affected its performance or longevity.

And with today's LED lights they are polarity sensitive like radios.

Gerald J.

Nope. It's either inertially or magnetically driven. All you have to switch to positive ground on that diagram is reverse the battery leads, swap the ammeter connections and repolarize the generator. Actually you don't have to reverse the ammeter, but you'd have to know that - means + and + means -.

you should have a 12 volt regulator.. some were OK for pos or neg ground... it might be printed inside the cover... You need to "polarize" the charging system once to tell the system how you have it connected... Normally taking a jumper wire and flashing the B and G terminals for 1 second will do that.

Unless someone has changed it to electric, it has a mechanical temperature gauge as indicated on the wiring diagram you posted. The ammeter should be the only electrical gauge on the tractor.

Jim.ME wrote: Unless someone has changed it to electric, it has a mechanical temperature gauge as indicated on the wiring diagram you posted. The ammeter should be the only electrical gauge on the tractor.

This being the advantage of negative ground. If you ever need to replace a gauge, electric gauges are more readily available. Most are negative ground.

That's okay if you check the specific gravity going into the winter. Let it go too low while there's a nasty arctic front passing through and you might end up with a frozen battery.

I'm glad to know that I'm not the only operating without an functioning charging system.  Almost rebuilt it this spring but the tractor only operates 6 or 8 hrs a week during the mowing season.  A battery tender to the rescue.  Works fine and the battery is removed and stored during winter.  It's made it 10 years that way.

Did you get a spark when you polarized?

I don't know what is "loose" on your starter solenoid... There should be a small and large wire on the back that are TIGHT on the terminals, and a strap that connects the solenoid to the starter... all studs should be TIGHT.... if there is a cover on the other end that is loose, that may or may not be a problem.

Where is the regulator located?

The jiggly doo-dad is from the solenoid on the starter to like a cam switch of some kind, which has a slot in it and the end of the solenoid but is loose in the cam slot, it's the opposite end from the terminals. I'd expect it to engage the gear for the starter, and that always clicks, but sometimes it doesn't connect 12V across the solenoid, so the motor don't spin.

This is the diesel D17, a 1957 if it helps. I can snap a pic of it tomorrow, no light in the shed. How do those starters come out? 1,2,3 or 4 bolts?

Sorry, I'm faultfinding both the charging and starting at the same time, hence the unrelated questions.

Edited by Coke - 03 Oct 2018 at 8:33pm

You description sounds like the lever that moves the starter drive to engage the ring gear is exposed on that starter. If that is the case that lever will have some play. When you turn the key to start the solenoid should receive power to turn it into a magnet. It should pull the plunger inside it forward, causing a plate inside the solenoid to make contact between the large solenoid terminals, supplying power to turn the starter motor. At the same time the solenoid should pull the lever with it moving the starter drive into mesh with the ring gear. If all the connections are good, you are sure it is not loosing voltage or ground when you engage it, and the solenoid is clicking; you may need to pull the starter with the solenoid on it and have them gone through or replace them. Find your starter at the AGCO parts books on line and it will help you identify the "jiggly doo-dad", for others.


I don't know about a D17 but on a D14 the voltage regulator is behind the panel on the left side of the tractor, under the fuel tank.

DougS wrote: Did you get a spark when you polarized?

Yes.

I'm gonna go out on a limb here, and say I found the problem.

That center washer is the contact point (I reckon), when the solenoid energizes, it gets pushed agains the contact points of the two bolts. Given that it, and the bolt bottoms are black with crud, I'm going to say that's where I've been losing the connection, the two shiny points must be my intermittent.

A few minutes with a dremel, and everything is nice and shiny again, and a bit of epoxy seals the crack in the case for now. We'll see if it works, and if it lasts. It's too wet right now to go out and fit it all back in the tractor.

Worst case scenario, a new one is $20 on eBay.

Yeah, I'd have been more tempted to take it apart if it didn't have a weird 5-pointed screw holding it together. I just cleaned it and the bolts up with a dremel, sealed the crack in the plastic cap, and put it all back together.

So far, it's started everytime.

Edited by Coke - 07 Oct 2018 at 6:30pm