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John Deere Tractors Discussion Board

Re: 4020 24 volt system dash lights

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Posted by Tom 43 on January 02, 2013 at 11:10:03 from (

In Reply to: 4020 24 volt system dash lights posted by 8850dave on January 02, 2013 at 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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