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John Deere Tractors Discussion Forum
Show Parts for Model:

4020 24 volt system dash lights

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8850dave

01-02-2013 04:34:27
198.229.217.179



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I bought 4020 last summer and have installed new wiring harness, but now oil and generator lites will not light unless I use test light inside power side and test lite is grounded and then the lights come on. Any ideas?




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Tom 43

01-02-2013 11:10:03
70.128.115.57



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 Re: 4020 24 volt system dash lights in reply to 8850dave, 01-02-2013 04:34:27  
The generator light is fed from the negative terminal of the battery, then to the switch which contains a resistor, then to the GEN light, and then to the GEN terminal of the voltage regulator which in turn goes to the output terminal of the generator. When the switch is turned on, current flows as described above to the generator output terminal and through brushes, through the armature and then finds ground back at the positive terminal of the second battery. The purpose of the resistor is to enable the use of a 12 volt bulb for the GEN light instead of a special 24 volt bulb.

To trouble shoot the generator light circuit, 1) Unhook the wire at the GEN terminal of the regulator that goes to the GEN light. Place the positive lead of a voltmeter on the positive terminal of the second or ground battery. 2) Connect the negative lead of the voltmeter to the unhooked wre going to the GEN light 3) Turn the switch on and you should read 24 Volts. 4) If you don't, keep reading backwards through the circuit with the negative lead of the voltmeter until you do.

To check the oil light, check the integrity and continuity of the small wire that goes from the tractor frame to the center of the two batteries. 2) If the wire has continuity, unhook the oil light wire at the oil pressure sending unit. Place the positive lead of the voltmeter between the batteries and the negative lead on the unhooked wire from the OIL light. Turn the switch on and you should read 12 VOLTS. 3) If you do read 12 replace the sending unit. 4) If you don't back track the oil light circuit with the negative lead of the voltmeter until you do and fix the problem.

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JD Seller

01-02-2013 07:12:25
208.126.196.144



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 Re: 4020 24 volt system dash lights in reply to 8850dave, 01-02-2013 04:34:27  
I would bet that you have the wrong dash harness. They where 6 or 7 different ones used originally. I think JD has substituted them down to three. So you will need to get a good wiring diagram and make yours correct.

I would bet that Tim is correct in that you have two grounds going to the dash lights.

Also make sure you have the correct ground/positive at the breakers on the back of the dash door. If you have them hooked up wrong they willmake the dash and lights not work correctly.

It makes it easier If you think of the system as being two separate 12 volt systems. One being negative ground and the other positive ground. Nothing on the whole setup sees 24 volt other than the starter and generator.

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Tim S

01-02-2013 07:30:33
75.49.13.105



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 Re: 4020 24 volt system dash lights in reply to JD Seller, 01-02-2013 07:12:25  
Yes jdseller that is a good way of saying it, and I"ll add that the system will need to continue seeing 2 12 volt feeds only now they will both be neg ground, so battery A&B switch post will both be positive when tested . this is the same on the new Gen switches too, they have 2 12 volt feeds to spread the power load, if only 1 has power only about half the stuff will work... If you tie the Blue and Brown wires together down at the starter to the 12 volt terminal it will take the feeds to Battery A&B at the switch, and this would be a good place for a circuit breaker if you don"t already have 2 from the old 24 volt system, those are good and also pricy, so save them...

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Cliff Nelson

01-02-2013 05:57:11
69.21.97.161



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 Re: 4020 24 volt system dash lights in reply to 8850dave, 01-02-2013 04:34:27  
It's your 24 volt system messing with you. lol. Seriously, it sounds like some wires may be switched. If you are testing the "power" side and getting the lights to work you have power to the sensor side. A good wiring diagram and understanding of the 24 volt system will help. Check with a volt meter to see if you have +12 or -12 volt in the right place. Also check for voltage at the oil pressure sensor. Probably a simple fix but difficult to find. Good luck.

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John T

01-02-2013 04:37:39
216.249.82.117



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 Re: 4020 24 volt system dash lights in reply to 8850dave, 01-02-2013 04:34:27  
You may want to insure theres a small jumper wire (and if fuzed its good) from the mid tie point of the two batteries to frame ground. Thats where they join in series in the middle NOT either of the two outermost + or - that go to the starter.

John T



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8850dave

01-02-2013 04:51:09
198.229.217.179



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 Re: 4020 24 volt system dash lights in reply to John T, 01-02-2013 04:37:39  
I have new cables and did put slow blow fuse assembly on the lh rear post.



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Tim S

01-02-2013 06:40:36
75.49.13.105



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 Re: 4020 24 volt system dash lights in reply to 8850dave, 01-02-2013 04:51:09  
You will need to change the wiring a bit,,getting 12 volt to the one side of the indicator light and letting the wire coming up from the oil sender be the ground, the way your hooked up now you have 2 grounds going on,, Like Clif said the 24 volt stuff is still messing with you, they are a strange and unfriendly system....I do away with all of them I can....



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