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John Deere Tractors Discussion Forum
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extra wire from distributor

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55 50

11-18-2006 10:36:23




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Recently repaired the lights on a 720 and noticed there was a wire from the + side of the coil back to the ignition/light switch, in addition to the wire going to the distributor. This wire isn"t on my 50. The "normal" ignition path is to the - side of the coil. So I went to the JD Electrical Systems Service Manual and reviewed those diagrams and find they show that wire for my 50 too. It must serve as the ground for the ignition while the switch is off. In the past, I"ve noted that mine will start with the ignition switch off [when I forget to turn the switch on!], (the ignition path is then from the "other" side {hotter side?} of the ignition resistor) but the tractor stops as soon as the starter button is released. If this additional wire was on my tractor, I suspect it would not start with the ignition switch off. I don"t plan to add this wire, just wondered if someone would verify if my thinking is correct here. I"ve never checked but assume my tractor does have a 6 volt coil, because it does have the ignition resistor and it starts and runs just fine.

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John T

11-18-2006 12:18:32




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 Re: extra wire from distributor in reply to 55 50, 11-18-2006 10:36:23  
55, I believe I can tell ya what n how Mother Deere used that wire n switch.

Okay, it was for TWO purposes. One if it had a Magneto ignition that MAG switch terminal wired down to the kill switch stud like used on Wico X mags to kill the spark when the ignition was OFF (by grounding that circuit) but unground/open it when ON so the Mag produced spark.

On battery powered coil ignitions that used an external ballast resistor and the ballast by pass circuit a safety problem was while the engine was cranking the ignition could still produce a spark even when the ignition was off SOOOOO OOOOO that extra lil wire off the switches MAG terminal wires down to the low (to distributor) side of the coil and provides a safety ground to kill the spark when the ignition is OFF yet the starter was depressed but is open so the engione runs when the ignition is ON.

Seems like that was kinda how you had it figured..... .... yep, if its a 12 volt tractor and has an external ballast resistor the coil is indeed a 6 volt coil. When cranking the extra lil side terminal on those mechanical start switches is hot which sends hot unballasted voltage to the coil n by passes the ballast for better starting spark. Buttttt without that MAG wire switch terminal she still fires even with the ignition OFF. Id fix n use it that way for safety if it were mine.

John T

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55 50

11-18-2006 18:15:50




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 Re: extra wire from distributor in reply to John T, 11-18-2006 12:18:32  
John, We"re thinking along the same line except now you got me to thinking further and that can be dangerous. You mentioned Wico X mags, but my 50 Parts Catalog lists only Wico and Delco Remy distributors. Would that numbered series ignition/light switch have been used elsewhere with a mag, hence the "mag" marking on the tractor wiring diagrams?

(the mystery deepens)



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F-I-T

11-18-2006 18:58:59




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 Re: extra wire from distributor in reply to 55 50, 11-18-2006 18:15:50  
Not to hijack a thread, but remember there were some wiring changes that took place with the introduction of the LP engine at 5024000, and I think that is when they added that wire, both as a saftey on gas and all-fuel engines, but also as a safety for the yet to be understood all too well, LP engines. Wish I had an older, earlier change letter parts book to verify that. Also, the magneto was available on the '50'. I think it was a no-cost option, and a lot of farmers familiar with mags, or who had the need to hand crank them when the hired help let the lights on, did indeed order them with mags. Mags were available into the -30 series, too.

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John T

11-19-2006 08:28:44




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 Re: extra wire from distributor in reply to F-I-T, 11-18-2006 18:58:59  
I also think or heard somewhere the Wico X Mag was a possible option on the 50 series as those tractors still had the side governor flange mount ignition (Mag fits right in no problem) versus the 20 series with the cam driven distributors.

Hijack Shmijack NOOOOO OOOO Problem, I alwaysssss ss appreciate and also provide inputs on any thread where we can all learn n help each other.

John T

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55 50

11-18-2006 21:17:12




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 Re: extra wire from distributor in reply to F-I-T, 11-18-2006 18:58:59  
That"s the kind of info I relish. It fills in a lot of the mystery. Thanks Frank.



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Gerald J.

11-18-2006 11:33:27




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 Re: extra wire from distributor in reply to 55 50, 11-18-2006 10:36:23  
The extra wire comes from the start switch or (for my 4020 from extra contacts on the starter solenoid) to apply 12 volts to the coil for better starting when the starter draws the battery way down. My 4020 did exactly as your tractor did when the ordinary ignition supply opened from a corroded Scotchtap. It would run while cranking but die as soon as I got off the starter button. I had to hot wire it that day to finish the hay. So you are using a 6 volt coil with resistor on a 12 volt system and it works fine.

Gerald J.

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55 50

11-18-2006 11:58:15




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 Re: extra wire from distributor in reply to Gerald J., 11-18-2006 11:33:27  
The extra wire I"m speaking about goes between the distributor side of the coil and the ignition switch terminal marked "MAG". It is not the wire that provides the 12 volts for the "boosted" ignition during starting. My tractor does have that "boosting" wire, but not the distributor-to-ignition wire. It is shown quite well in the wiring diagram in JD Manual SM-2029.



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55 50

11-18-2006 10:38:11




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 Re: extra wire from distributor in reply to 55 50, 11-18-2006 10:36:23  
Sorry, my title should have said "from coil".



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