Electrical problem, early 4020D

Couple weeks back I asked some questions about electrical issues with an early 4020D. It was new to the owner so he knew very little of it. The batteries looked new but were old and dead as bricks. The generator too appeared to be a new rebuild with a genuine JD sticker on it. The battery cables looked new but the string's polarity was opposite how it left Waterloo and absolutely nothing worked but half the lights.

What I did was I reversed the battery string so the polarity matched how it left Waterloo. Still nothing. Found the side post of the starter was NOT making contact with the cable. Fixed that & then he would start. It did not charge and the fuel gauge started to work. I assumed the generator was not properly polarized and having heard so many horror stories about them I sought advice.

I decided to let you fellers know how it all worked out. The generator light worked after reversing the batteries as did the fuel gauge but the lamp got brighter as the engine speed was increased. That told me the generator was working but something was not right. Again I assumed polarity so I tried to polarize it. Scratched the BAT lug of the regulator to the ARM lug. Hmmmm. No sparks. Seemed dead. After checking all the wiring harness plugs (cleaning and straightening) and the back of the kick panel (which was beautiful except for dust) nothing was found out of place! Testing still showed the right battery at the regulator on the GRD terminal of the regulator but the BAT terminal appeared open between the regulator and the battery. Wiring harness looked good. No cuts, nicks or tape nor any visible damage. Discussed the matter with the owner before ripping deeper into the harness but he agreed..... Must be something hiding in there. We stripped the harness from the regulator back to the starter & found a flattened spot on the wire where it crossed behind the engine to the left side of the tractor. Just looked like slightly pinched plastic but a little tug on the wire and it popped in two. Nothing inside this leetle tiny blue tube but green powder for about 3/8 of an inch! A few inches down the line was another just like it.

Fixed those with a new section of blue wire cleaned, crimped, soldered and taped it all three ways from next Sunday and put it all back together. A swipe from BAT to ARM gave some sparks and the armature rotated in the running direction. Buttoned him all up, turned on the key & the GEN lamp glowed with the same intensity as the oil lamp. Hit the starter, he took right off and the GEN lamp went out. Battery voltage went from 24.6 before we hit the starter up to 27.9 as the light went out. The lights all work and they're all the same intensity.

Seems like the actual problem in this tractor had apparently stumped someone else in years past and was not discussed here, just having the ability to boost a feller's confidence a bit is a great help and too rarely do those getting the help fail to send back thanks and appreciation. I'm sending mine.

Thanks and later!

The battery will appear open back to the regulator if the cutout contacts are open due to the generator not charging .
I used to be a purist and believe a 24V new generation tractor should be left 24V.
Given the inherent design flaw of only using a single contact starter solenoid instead of a two pole starter solenoid contact design. And how the typical tinkerer is challenged with the -12V/+12V/24V floating system.

Perhaps ordering a wiring kit from Jim at https://www.wiringharnesses.com/ would save a lot of aggravation . And a 4Kw or better yet a 5Kw starter from Iskra in 12V.

GOOD JOB, Al, and CONGRATULATIONS!

You have proved all the naysayers wrong that like to ramble about these systems being nearly impossible to fix!

I think 24 volt systems are not impossible to repair. I think 24 volt systems are more prone to problems then 12 volt system & are more complicated to diagnose for problems especially for people that don't fully understand the JD 24 volt system.
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Due to the fact that 12 volt batteries have higher cranking amps & 12 volt starters are more powerful than 50 yrs ago if I owned a JD tractor with 24 volt system I'd change it to 12 volt system the 1st time the electrical system gave me a problem.

A few yrs back I diagnosed/repaired several JD 24 volt system

I forgot to congratulate buckeye al on his successful 24 volt
electrical repair

Your efforts go to show these simple systems can be repaired if you put a little thought and determination into it. Good job diagnosing and Thank you for sharing your experience!. DW

Yes, very good Buckeye! I like to hear of success with 24 volts. I have a sweet 4010D/24 volt and we all cherish it. My guys like it and will jump on it more often than a cab tractor. I had gone through the whole electrical system, rebuilt everything. Works likes a charm. Twenty-four volts is like a strange relative. You just have to have patience and understand it.

Excellent catch to find that fault buried in the wiring harness .