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Gents, I have a 1964 4020 with the original 24 volt starter. Recently, after trying to start the tractor I noted the starter ran on after I released the key from the start position. The only way to stop the starter from turning was to removed the left battery terminal which resulted in a large spark. When I immediately tried to put the cable back on the battery post again it sparked. After a minute or so I was able to again install the battery cable on the post. It appears that the solenoid is sticking but thought I would get some opinions prior to disassembling. In reading the schematic +12 VDC goes to the G terminal on the solenoid and the S terminal goes to the "S" terminal on the switch. I'm not sure whether the S terminal on the switch provides a ground path or how the solenoid is activated.

Any ideas?
 

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24 volt solenoids on JD tractors have a long history of the washer & lugs inside of solenoid getting pitted and sticking. On some solenoids the end cap can be removed and washer flipped over. At the same time the lugs can be filed smooth. In rare cases low battery voltage can cause starter solenoid to hang in also.
 

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The yellow wire is grounded when starting. Another item I have seen is a neutral start switch or neutral start harness can short to ground to cause starter to stay engaged.
 

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The yellow wire is grounded when starting. Another item I have seen is a neutral start switch or neutral start harness can short to ground to cause starter to stay engaged.
jd110
Sorry but I disagree. JD 24 volt system starters,generators & regulators are isolated from frame IE no ground for starting circuit. The yellow wire attached to "S" terminal is completing the 24 volt circuit but has nothing to do with any type of ground connection. Back in the 4020's heyday I spent many hrs diagnosing 24 volt systems problems when I was a JD dealer service manager.
Jim
 

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TxJim, technically you are correct that starting circuit is isolated from ground and no ground to frame is needed to start. I shouldn't have stated it that way. I do know that if the circuit between the starter and the neutral switch shorts to ground, the starter will crank. That starter push button connects the yellow wire on the starter to the negative side of the left battery to crank.
 

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TxJim, technically you are correct that starting circuit is isolated from ground and no ground to frame is needed to start. I shouldn't have stated it that way. I do know that if the circuit between the starter and the neutral switch shorts to ground, the starter will crank. That starter push button connects the yellow wire on the starter to the negative side of the left battery to crank.
Technically I think if a grounded push button switch on dash engages a JD 24 volt starter then something is wrong with wiring in that it has been altered from factory. As I previously stated pushing switch button on dash should complete the 24 Volt circuit to engage solenoid. If one looks at solenoid mounting bracket it will have 24 V stamped on it.

You agreed with me that starter & generator circuits are isolated from tractor frame IE no ground connection so how is a ground connection going to engage starter?????????:dunno:

I fail to see by viewing wiring schematic how on a factory wiring that yellow wire is attached to negative post on LH battery. The blue & brown wires are the supply wires for the A & B circuits of the 24 volt system.
 

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Jim, I didn't mean to say the yellow wire was physically connected to the battery. The left negative cable connects to the top starter terminal. The blue wire also connects to the same terminal. The blue wire then attaches to the key switch. When the key switch is turned on, internal contacts connects the blue circuit to the starter button when starter button is engaged, it connects that same blue circuit to the neutral switches and then to yellow wire on starter. In that way, the yellow wire is connected to the battery through safety's witches, push button switch, key switch, and then the blue wire to starter. Sorry if I oversimplified my statement. As far as grounding the yellow wire engaging the starter, I can't explain why, but I have seen it happen on more than one occasion. Maybe the occasions I have seen it, there were other underlying problems( you have to admit there are many possible things that went wrong on the 24 volt systems) . One of the challenges with them is finding a electrical shop that understood proper way to rebuild the country he starter and generator and not to try substituting 12 volt parts on them. I have seen more than one that had a 12 volt solenoid bolted on and it might start if you are lucky, but it would create a drain on the system since it wasn't properly insulated from ground.
 

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jd110
I knew what you were referring to BUT you utilized the word "grounded" which IMHO is incorrect because joining two 12 volt circuits doesn't involve grounding any more than joining two 120 volt AC circuit to create 240 volts AC. I agree JD 24 volt systems are difficult to understand & diagnose for the general public. If I owned a JD tractor that came with 24 volt system it would be changed to 12 volt system ASAP and I know how to diagnose/repair the 24 volt system but choose not to.
 
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