Switching over a john deere 4020 from generator to alter

I'm having a problem with my john deere lp 4020 I'm switching it over to alternator, with the generator it starts up when I switch to alternator it turn over but doesn't fire I switch the battery terminal to pos pos and neg to neg iv run a hot wire from the battery to the alternator ive switch out the coil everyone I have talked to say that should be good, but it's not firing, anyone got any suggestions????

run hot wire to ignition side of coil try starting it. usually
changing polarity screws things up unless you pre arranged
change. alternator regulater might be toast.
batterys unhooked install alt. if tractor was pos ground switch
battery posts reversing to neg ground. then switch coil wires .it
should be right.
you could fried ignition post on key switch

(quoted from post at 05:43:13 02/16/23) I'm having a problem with my john deere lp 4020 I'm switching it over to alternator, with the generator it starts up when I switch to alternator it turn over but doesn't fire I switch the battery terminal to pos pos and neg to neg iv run a hot wire from the battery to the alternator ive switch out the coil everyone I have talked to say that should be good, but it's not firing, anyone got any suggestions????

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Are you converting from 24 volt to 12 volts? If it was 24 volt the system is split, and it may require more than just swapping battery terminals around. Post this down on the John Deere Forum. And give all the info regarding what it was and what you are converting to. There are some fellows there very familiar with making that swap.

John Deere Forum

Hello SW welcome to YT! What Jim said is exactly
correct you need either a 24 volt alternator or a 12 volt
starter. Being an IH guy I cannot tell you exactly what
you need to do the JD guys will help you there. I just
want to warn you to be careful how you have the
batteries hooked up in relation to the alternator what
rb posted was a little confusing and I do not think
applies to your situation. Just do not connect the
alternator and have the tractor positive ground or you
will fry it.

An ignition coil will still fire even with the polarity reversed.

Does it still have points? If it has been converted to electronic ignition, those are polarity specific, and not reversible.

I would double check the wiring, possibly a wire got left off when the polarity was switched, somehow it is now not getting power to the coil.

Deere GAS 4020's were never 24 Volt.

(quoted from post at 09:03:42 02/16/23)
Deere GAS 4020's were never 24 Volt.

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Thanks, rules that out.

First of all, the 4020 Gas or LP was 12 Volts (ONLY Diesels were 24 Volt) and far as I know (NO warranty)
as long as they still used generators instead of alternators they were originally POS ground.

NOTE if you convert to Alternator most all are NEG Ground, so if the tractors was POS ground you need to
reverse the polarity for NEG Ground. I hope the alternator wasn't damaged !!!!!!!!

The big main alternator charge wire output (for Neg ground tractor and alternator) would connect to the
batterys POS post

To change from POS to NEG ground the coils wires would be swapped HOWEVER it will still fire even if
incorrect polarity

If all else is well but theres no fire work through my Troubleshooting Procedure to find the problem, so
often its simply the points

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=ttalk&th=2060825

PS best I recall there was something else different on LP tractors but I forget what it was ???????? I
still thought all were 12 Volts and as long as a generator was used still POS ground original MAYBE AN
EXPERT CAN CONFIRM OR REBUT THAT ???????? When they went to alternators then it was NEG ground

John T
John Ts Ignition Troubleshooting

Sorry for the misinformation SW. My main purpose of
posting was to warn you about possible damage to the
alternator with a reverse polarity, should have stuck
with that. Thanks for the correction guys!

(quoted from post at 06:03:42 02/16/23)
Deere GAS 4020's were never 24 Volt.

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Mine is LP

It is electronic ignition

If u remember please let me know thanks

You have now stated that it has electronic ignition.

Electronic ignition modules are built for one polarity or the other and are usually destroyed if the system polarity is swapped

So if the module you have is for the original (+) ground system and you are changing to (-) ground you will need to swap the (+) ground module for a (+) ground unit.

If its EI they must have the correct polarity and if not it may be fried. See below where I stated they
were originally POS Ground as I recall

John T

If you accidentally connected a NEG ground Electronic Ignition to POS Ground (what tractor was original) it
may have been damaged ??? With an alternator, as most are NEG Ground, the tractor needs converted over to
NEG Ground and likewise the EI be for Neg Ground. When the IGN is turned on there should be 12 volts getting
to the coils input that has to happen before you will get spark. You have to insure you changed to NEG
Ground,,, the Alternator is NEG ground (which most are),,,,, ,,,the EI is for NEG Ground,,,,, ,,The coil
wires should be swapped (when converting to NEG Ground),,,,, ,,,12 volts is getting to the coil when IGN is
ON,,,,, ,,Try my Troubleshooting Procedure for no fire

John T