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John Deere Tractors Discussion Forum
Show Parts for Model:

720 gas tractor

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WTM8

10-10-2018 16:26:50




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Yes, the points are sparking when cranking with the distributor cap removed and ignition off. No, it doesn't continue to run when the ignition is turned off. No. it doesn't pop or backfire when the ignition is turned off. I didn't check the plugs yet.




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buickanddeere

10-12-2018 05:52:07




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 Re: 720 gas tractor in reply to WTM8, 10-10-2018 16:26:50  
Quoting Removed, click Modern View to see

The double post is in the JD section of the YTMAG site not a crisis .
The wiring mess in the 720 is a barn fire crisis waiting to happen . The most humane , lowest cost , most reliable and quickest solution . Would be to have a knowledgeable person install a 100% new wiring harness , probably gauges , probably refurbished generator and a probably a refurbished starter. Along with a new battery box , a new group 31 battery and new HD cables . Jim at http://www.wiringharnesses.com makes the best for a modest fee.

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buickanddeere

10-11-2018 10:00:54




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 Re: 720 gas tractor in reply to WTM8, 10-10-2018 16:26:50  
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Not to worry and it is not a crisis . I just wondered if I was seeing double .



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John T

10-12-2018 04:51:54




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 Re: 720 gas tractor in reply to buickanddeere, 10-11-2018 10:00:54  
Hey there Glen, I disagree with statements below along the lines of its normal or its nothing to worry about. If my recollection is correct ITS NOT NORMAL AND IT IS INDEED SOMETHING TO WORRY ABOUT.

As I recall and understand if it as the CORRECT ignition switch (has extra Mag/Ground terminal wired to coils output) and iffffffffff it is wired CORRECT, when the Ignition is OFF if the starter motor is cranked, THERES NO SPARK AND NO FIRE.

Sure, it can still "work" with the wrong or miswired switch BUT ITS A SAFETY HAZARD, NOTTTTTTTTT NORMAL, AND IS SOMETHING TO WORRY ABOUT Deere had a reason for adding that safety feature and for use of the ignition switch and its Mag/Ground terminal wired down to the coils output SO THERE COULD BE NO FIRE IF CRANKED WITH IGNITION OFF.

When I was a used tractor dealer and farmer in those days and used those tractors I saw many repairs and jury rigs with the wrong switch or miswired and if his ignition is hot with ignition off while cranking ITS NOTTTTTTTTTTTTT FACTORY ORIGINAL NOR CORRECT as I best recall.

See my post and explanation below

What are your thoughts on this and safety ??????????????

John T Retired Electrical Engineer

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buickanddeere

10-11-2018 06:46:30




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 Re: 720 gas tractor in reply to WTM8, 10-10-2018 16:26:50  
Quoting Removed, click Modern View to see. Why two posts on the same topic ?



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WTM8

10-11-2018 09:10:24




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 Re: 720 gas tractor in reply to buickanddeere, 10-11-2018 06:46:30  
Sorry, but my wife is not used to doing things like this on the computer and she made a mistake. If this causes a problem you can take off the last one. Thanks.



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John T

10-11-2018 04:52:53




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 Re: 720 gas tractor in reply to WTM8, 10-10-2018 16:26:50  
With all due respect to James and Lee, let me offer a somewhat different response, maybe right maybe wrong, its based on olddddddddddd recall lol so NO WARRANTY. I believe there's a safety related reason for FOUR wires to the coil NOT just 2 or three, and if wired correct to the correct ignition switch IT SHOULD NOT FIRE WHEN CRANKING WITH IGNITION OFF IE

ITS NOTTTTTTTTTTTTTTTT NORMAL AND DOES (or should be for safety and originality) NEED FIXED !!!!!!!!!!!!!!!

IFFFFFFFFFFF its wired CORRECT with the CORRECT ignition switch ..

a) With Ignition ON when cranking the ballast is by passed so there's unballasted battery voltage getting to the coil via the extra little terminal on the starter switch so the points would spark and the coil produce a spark........Thats the ballast by pass while cranking system used with a 6 volt coil on a 12 volt tractor to produce a hotter spark when cranking to help in cold weather starting.

b) With Ignition OFF when cranking if its wired CORRECT with a CORRECT ignition switch THE POINTS SHOULD NOTTTTTTTTTTTT SPARK That's a safety design so if a person engaged the starter with the ignition OFF it wouldn't spark when cranking

HERES HOW IT WORKS AND WAS DESIGNED AS I BEST RECALL

I believe there are FOUR wires TO the coil (even if one is from ballast where it wires to coils input).

1) On INPUT from ignition switch one wire is hot when ignition is ON 2) On INPUT (or ballast terminal that wires to coil) there's a wire to the small side terminal on the starter switch which is hot ONLY while cranking to by pass the ballast while cranking. 3) On the coils OUTPUT there's a wire to the distributor which leads to the points inside. 4) On the coils OUTPUT theres s wire up to the MAG/GROUND terminal on a CORRECT ignition switch so if its cranked with ignition OFF the coils output is safety grounded (effectively shunts across points) so there's no fire and the points should NOT spark.

Thats the reason for FOUR wires on the coil, 2 on INPUT (or one to ballast which wires to coil) and 2 on OUTPUT. Normally the OUTPUT just has one wire to the points but for safety to prevent fire when cranking with ignition OFF you need the extra safety wire to a CORRECT ignition switch which grounds the points (direct path from coil output to ground) when cranking if ignition is OFF

MY BEST GUESS FOR WHY POINTS STILL FIRE WHEN CRANKING WITH IGNITION OFF

A) Wrong ignition swtitch with no MAG/GROUND terminal down to the coils OUTPUT..... B) Wire is missing or disconnected FROM coils OUTPUT TO MAG/GROUND terminal on ignition switch. C) Ignition switch is bad or not well frame grounded..... D) Incorrect Ignition switch missing the Mag/Ground terminal I believe the correct switch had the Mag/Ground terminal which grounded out a mag if a mag was used instead of a distributor and the ballast and ballast by pass.....

TROUBLESHOOTING Insure you have the correct ignition switch,,,,,,,,,,,,,, with the extra Mag/Ground terminal that's connected to the coils output,,,,,,,,,,,Insure the coil has two wires on its OUTPUT

John T

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451 CUBES

10-12-2018 16:22:20




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 Re: 720 gas tractor in reply to John T, 10-11-2018 04:52:53  
John T

Your safety grounding wire looks to be the brown on Mr. Howell's diagram? If so, your recollection sounds correct and makes sense.



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James Howell

10-10-2018 21:16:58




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 Re: 720 gas tractor in reply to WTM8, 10-10-2018 16:26:50  
"Yes, the points are sparking when cranking with the distributor cap removed and ignition off."

Agree with Lee B's statement "Your tractor has been set up with the popular ballast resistor bypass for starting only option".

Take a look at the diagram below.

Note the black wire that is connected to the starter switch and ignition resistor.

Take a look at the photos below.

Note the side terminal on the starter switch.

Note the black wire connected to the side terminal on the starter switch leading to the ignition resistor.

Note the black wire from the starter switch connected to the "output" terminal on the ignition resistor.

When you press down on the starter pedal, 12 volt power temporarily goes directly from the battery to the ignition resistor and coil at start up.

Take a look at the diagram below.

If the ignition switch is ON, then once you release the starter pedal, the power comes from the ignition switch to the ignition resistor and coil.

Hope this helps.

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Lee B

10-10-2018 17:27:29




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 Re: 720 gas tractor in reply to WTM8, 10-10-2018 16:26:50  
Your tractor has been set up with the popular ballast resistor bypass for starting only option then.

This involves a second feed for power coming from the starter solenoid such that when the starter is engaged you are sending 12 volts directly to the coil which helps at a time when battery voltage is drawn low by the load of the starter itself. This connection is usually on the opposite side of the solenoid from the one that activates the solenoid.

It is normal to see that, no need to fix it.

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