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John Oliver
John Oliver,
Category: Agriculture and Farm Equipment
Satisfied Customers: 201
Experience:  manager at White Eagle Ag and Truck Services
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I have a 1965 JD 4020. The start button quit, so I have been

Customer Question

I have a 1965 JD 4020. The start button quit, so I have been using the screw driver method to start the tractor. Now that won't work. Both batteries tested good and show more than 12 volts. I don't know if varmints got to the wiring or not. I cannot see anything chewed up anywhere. I cleaned the battery terminals. The solenoid clicks a engages the starter but not enough umphs to get it to turn over
Submitted: 1 year ago.
Category: Agriculture and Farm Equipment
Expert:  John Oliver replied 1 year ago.

hello Ron my name is ***** ***** you tested to see if you have power on your small signal wire at the starter solinoid?

Customer: replied 1 year ago.
it shows 12 volts
Customer: replied 1 year ago.
all terminals on the starter (Battery, and solenoid) show 12 volts.
Customer: replied 1 year ago.
All terminals are hot even with the key in the off position.
Expert:  John Oliver replied 1 year ago.

what we are only concerned about is the small signal wire on the starter when the key is put into the start position

Customer: replied 1 year ago.
As I said earlier, all terminals on the starter ( the two poles on the solenoid and the battery cables show twelve volts, - key on or off.
Expert:  John Oliver replied 1 year ago.

i would say that is your issue. if that small wire is hot all the time it must have energized your starter for an extended period of time and burned it up. first before replacing the starter you are going to want to figure out why that signal wire is hot all the time. (starter relay or key switch) maybe recheck your diagnostics just in case but that small wire all by itself should only have 12 volts when the key is turned to "start"

Customer: replied 1 year ago.
The starter and the starter solenoid work fine as I can still start the engine using a screwdriver across the terminals. The problem is I can't seem to find out why everything is hot all the time. Any suggestions?
Expert:  John Oliver replied 1 year ago.

well, again if all wires were hot the starter soinoid would engage. are you using a test light? if so your grounding the light to the tractor frame correct? i have a feeling that your test results are not correct and that is what is throwing us off. there are only 2 locations for wires on that starter. the one big lug that battery cables attach to and one small lug for the signal wire. do you agree?

Customer: replied 1 year ago.
No, This tractor has the 24 volt system. There are 2 battery posts going to the stater + & - and two terminals on the solenoid. Each post indicates the 12 volts - key on or off. It worked fine and then one day the starter button failed to start the tractor, hence the old screw driver trick which still works. I have used a test light and volt meter to ascertain just what is going on and I am stumped.
Expert:  John Oliver replied 1 year ago.

so the screw driver is crossing the main starter lug to the small wire on the solinoid correct? and that starts it fine?

i hate to keep asking to repeat yourself but it does not make sence that that small wire has 12 volts all the time.

Customer: replied 1 year ago.
You are right, It does not make sense. The only conclusion I have been able to come up with is the wiring harness has somehow been compromised. Would you agree?
Expert:  John Oliver replied 1 year ago.

ya to a dead short. but lets think about this, if that signal wire has 12volt now just sitting there.....why isnt the starter turning?

yet you apply a screw driver from the main lug to that same wire with the same 12 volts and it turns.....

heres what i think..... you are getting 12 volts on that signal wire but no amperage. i would focus your test light on the start relay. follow that wire and see if there is switched power at that relay

Customer: replied 1 year ago.
This being a 24 volt system and how it works is beyond me but I do know that there is a switch or contact somewhere that combines the two 12 volt circuits to make things happen. It may be that this switch wherever it may be is the root of the problem. Have you had any experience with this kind of system that may shed light on where one might find that switch.
Expert:  John Oliver replied 1 year ago.

do both positive cables attach to the same lug on the starter?

Customer: replied 1 year ago.
No two separate locations
Expert:  John Oliver replied 1 year ago.

1 hooks to the starter and the second hooks to where??

Customer: replied 1 year ago.
both hook to two separate terminals on the starter
Expert:  John Oliver replied 1 year ago.

i dont think your 24 volts. i havent ever seen one that was.... doesnt mean that somebody didnt install a 24 volt starter and alternator. the two 12volt batteries would need to be connected positive to negative. then negative ground to a single point positive on the starter. im quite certain your 12 volts

Customer: replied 1 year ago.
John This is a 1965 John Deere 4020 tractor. After 1965 they dropped the 24 volt system and went to the 12 volt system. It is unique to earlier big John Deere tractors and they have some idiosyncrasies.If you are not familiar with that type of system, it's hard to understand what the solution might be. The guys at the JD dealer are to young to know anything about this system. I don't think we are going to get to the solution of my problem. I have the repair manual with the wiring diagram and still can't figure out what is going on. Thanks for your input but I think it is time to move on.

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