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  1. #1

    Default John Deere 4020 Electrical Problem

    Hello all,

    Have a problem with my 4020.

    This past summer - if the tractor sat for more than 2-3 days...it wouldnt start. At the time - was a 24v system.

    1st thing I did was replace the battery's - 2 brand new JD 12v's.

    Seemed to help for awhile - but not long and was back to not starting if sat for more than a few days.

    After many suggestions to switch the tractor over to 12v- I bit the bullet and bought the kit. Switched her over didnt seem to have any problems. Followed the enclosed directions. Hooked the batteries up parrallel (Both pos to starter - both negs to tractor frame)

    Same thing - accept seemingly worse now. Tractor sits for one day..and it wont start without boosting. Hmmm.

    Started some trouble shooting. Hooked up a load tester. Both batteries showing 12-13 volts after a charge. Unhooked the red/white wire clip that goes into the alternator - checked with test light.....red = light, and white = dim light. To my understanding - with the key off....my white wire should be dead. So seem to have some stray voltage here?

    Went up to the key - all spades on back side are used. 3 of the 5 are hot with the key off. (one is quite a bit dimmer than the others)

    Is this telling anybody anything? I dont have a clue where to go next....but getting tired of having to boost every time I need to start the tractor. (Start every 3-4 days to fill a hayfeeder)

    *I purchased a new switch from JD today - and will install and report back.

    Thanks for any insight.

  2. #2
    Super Member flusher's Avatar
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    Default Re: John Deere 4020 Electrical Problem

    Quote Originally Posted by cornstalk
    Hello all,

    Have a problem with my 4020.

    This past summer - if the tractor sat for more than 2-3 days...it wouldnt start. At the time - was a 24v system.

    1st thing I did was replace the battery's - 2 brand new JD 12v's.

    Seemed to help for awhile - but not long and was back to not starting if sat for more than a few days.

    After many suggestions to switch the tractor over to 12v- I bit the bullet and bought the kit. Switched her over didnt seem to have any problems. Followed the enclosed directions. Hooked the batteries up parrallel (Both pos to starter - both negs to tractor frame)

    Same thing - accept seemingly worse now. Tractor sits for one day..and it wont start without boosting. Hmmm.

    Started some trouble shooting. Hooked up a load tester. Both batteries showing 12-13 volts after a charge. Unhooked the red/white wire clip that goes into the alternator - checked with test light.....red = light, and white = dim light. To my understanding - with the key off....my white wire should be dead. So seem to have some stray voltage here?

    Went up to the key - all spades on back side are used. 3 of the 5 are hot with the key off. (one is quite a bit dimmer than the others)

    Is this telling anybody anything? I dont have a clue where to go next....but getting tired of having to boost every time I need to start the tractor. (Start every 3-4 days to fill a hayfeeder)

    *I purchased a new switch from JD today - and will install and report back.

    Thanks for any insight.
    Don't have a circuit diagram for the 4020. Can't help you directly, but I have a suggestion.

    My 1964 MF-135 diesel is the same vintage as the JD 4020. The fuel sender unit is in series with the fuel gauge (which is an ammeter) which is connected through an oil pressure switch to the battery positive terminal. The pressure switch is open circuit when the engine is off and prevents the battery from discharging slowly through the fuel sender unit. When oil pressure is there the fuel gauge circuit is completed and the gauge reads the fuel level.

    Don't know if your 4020 has this type of setup or if the key switch provides the same function as my oil pressure switch. But I'd check out that key switch and also the fuel gauge circuit to see if the battery is discharging there.

    Hope this helps.

  3. #3

    Default Re: John Deere 4020 Electrical Problem

    Flusher:

    Thats very interesting that you mention this. Have been having trouble with my fuel gauge for as long as I've had the tractor - 1.5 yrs. This past summer I replaced the sender - thinking that would cure it. It did not -Used to be stuck at 1/3 tank now it is either pegged out, or it is completely zeroed out.

    Is there anyway to isolate the fuel guage circuit - to see if this is indeed the problem? I can live without the fuel guage as I have for the past year. Could always fix that later.

    Thanks for the help.

  4. #4

    Default Re: John Deere 4020 Electrical Problem

    Discovered a few things when I came home and took t he old switch apart. 1. The white wire spade was broken off from behind the switch. 2. Checked my wires for voltage with the key off- The blue, and brown are hot 12v's. I have a grey wire that is dim hot with my test light - meter showed 2v's. The rest of the wires were dead with the key off (grn, dbl black, broken white).

    Interestingly - I started the tractor up and ran the idle up a little - and checked that broken white wire behind the switch for voltage - nothing...dead. Put meter on battery's with tractor running - shows it's charging - 14.2v's. ??

    I also checked the current via positive terminal post - to positive cable with the tractor off. Showing a 10v draw.

    The isolator switches on the batteries appeared to work in preventing the draw - as I had 12.5 volts prior to starting the tractor - and was enough to crank er over. (Had sat overnight).

    I did post this on the tractors.net site also.

    Let me know if any of this is indicating anything to anyone.

  5. #5
    Veteran Member chh's Avatar
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    Default Re: John Deere 4020 Electrical Problem

    I sold my 4020 almost 10 years ago now. I just can't remember how the wiring was laid out. I had my 12V conversion done by a JD dealer so I'm not real familiar about exactly how it was done. Your voltages on charging and for the batteries after charging sound very good. A 10v draw is a pretty good amount. You could try disconnect the fuel sending unit or the wire from the back of the guage to check that.(Mine never worked) An isolator switch on the batteries or disconnecting the positive terminals(I had to do that on a Ford for awhile)would help on the short term until you could get it traced out. Do any of your lights work after the conversion? Mine didn't. Checking the wiring at the back of all the controls, guages, and starter looking for stray voltage is about all I can suggest.

    Sorry I couldn't be of more help.
    Good Luck
    Good judgment comes from experience, and a lot of that comes from bad judgment.
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    The farmer is the only man in our economy who buys everything at retail, sells everything at wholesale and pays the freight both ways.
    John F. Kennedy

  6. #6
    Super Member flusher's Avatar
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    Default Re: John Deere 4020 Electrical Problem

    Quote Originally Posted by cornstalk
    Flusher:

    Thats very interesting that you mention this. Have been having trouble with my fuel gauge for as long as I've had the tractor - 1.5 yrs. This past summer I replaced the sender - thinking that would cure it. It did not -Used to be stuck at 1/3 tank now it is either pegged out, or it is completely zeroed out.

    Is there anyway to isolate the fuel guage circuit - to see if this is indeed the problem? I can live without the fuel guage as I have for the past year. Could always fix that later.

    Thanks for the help.
    The easiest way is to be sure the battery is fully charged (put it on a charger if necessary). Then disconnect the fuel sender unit. On my 135 this is easy. Just remove the single wire connection to the sender unit (at the fuel tank end where the sender is located). Wait 2-3 days and see what happens when you try to start your tractor. If it starts, then you have a problem in the fuel gauge circuit and you need to find out how JD isolates the fuel circuit from the battery when the key switch is OFF.

    It'll probably be a bear to trace the circuitry under the dashboard so my first order of business would be to get a circuit schematic.

    Try Yesterday's Tractors website and check the JD forum. Search for "4020" and sort through until you find a thread on your problem. My guess is that you'll find several.

  7. #7

    Default Re: John Deere 4020 Electrical Problem

    Thanks flusher.

    Talked to my uncle about this last night - he has a 4020.

    He tells me the orange wire going to the fuel sender is a ground wire. When I told him the gauge was pegged out - he figured the wire was "shorting" out some place.

  8. #8

    Default Re: John Deere 4020 Electrical Problem

    Something on the tractor is going to ground and draining your battery over a period of time. Could be the switch that you found broken. The bestway to troubleshoot this is to fully charge the batteries, the set up your voltmeter to measure the amperage draw when the tractor is turned off. You should see some reading of current draw. Then you will need to start disconnecting the wiring harness one lead at a time and check the meter. If you see the current draw go down when you disconnect something, theres your problem (or part of it). If you go through the entire tractor and nothing seems to change, then you may have a harness that is shorting to ground somewhere. That's going to take some time to sort out. BTW, 14.2V charging means your alternator is working well.
    JD 2305, FEL, 647 tiller, 48" Box Blade, 62" MMM

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