630 JD wiring question for electronics wizards

Disclaimer: I am severely electronics challenged! However, I'm in the process of rewiring a 630 and have a question about the wire(labeled "10" in photo) from the starter button to the ignition resistor. This wire was not present on the tractor as I received it and it ran OK. Moreover, new (after-market) switches seem to have only two terminals, as opposed to three as shown in the diagram. What's the function of this wire and do I need to include it in the re-do? Thanks in advance for your comment.

I don't' have a diagram at hand, but I SUSPECT the wire in question keeps the engine from firing/starting while being cranked with the starter with the ignition switch in the "OFF" position.

Under those conditions, the coil receives power through the starting bypass, and the wire/extra switch terminal grounds the ignition system out at the points side of the coil.)

This is the wire that limits the power to the coil. It delivers full power while starting and as soon as the starter button is released it sends the power to the coil through the resistor.
New switches from Deere will have the third terminal. If you ever have a tractor that will start and then immediatly stop when you release the starter button you can be assured that the resistor has failed.

So it is a "limiting wire", then?

(quoted from post at 00:03:07 09/05/11) So it is a "limiting wire", then?

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Bob
How is that a "limiting wire" when it adds voltage?

I don't agree that the wire from starter solenoid to resistor limits anything but adds more voltage to give points 12Vs when starter is engaged. The resistor is the only limiting thing in the wiring.

Okay, Heres a 630 wiring diagram taken from the John Deere Service Manual SM 2029 I CANT GUARANTEE THATS HOW YOURE WIRED AS THOSE DIAGRAMS SURE ARENT PERFECT.

BUT IF THAT DIAGRAM IS CORRECT

1) The wire from a 3 wire starter button to the ignition resistor IS FOR A STARTING BALLAST BY PASS. It sends full unballasted battery voltage to the coil ONLY while cranking for a hotter starting spark. When its not present with battery voltage the coil (a 6 volt coil) only sees around 6 volts for normal running but ONLY when the button is depressed does the coil see unballasted battery voltage. That can help startign under extreme cold conditions.

2) The tractor can still start fine without that wire as the coil still has voltage via the voltage dropping (12 to 6) balalst resistor. HOWEVER if its real cold and/or the engine is weak it will start better with the ballast by pass in operation cuz it has a hotter spark when its needed.

3) There are other ways to achieve this, like an extra I terminal on a starter solenoid and on the 20 and older series tractors via an extra terminal (hot ONLY as cranking) switch on the mechanical push to engage starter switches...

Got it????????

John T

630 Wiring Diagram

Yo my friend Mayor Bob, what youre describing is how it was done on the 20 series tractors. They used a mechanical saddle mount push to start switch on the starter and it had the extra terminal (hot only when engaged) that wired to the coil to send unballasted batetry voltage to it ONLY while cranking. On those the ignition switch had an extra terminal marked MAG or grnd which wired to the low (to distributor) side of the coil so if it was cranked with ign OFF it couldnt fire. On the 30 series they used the push to crank switch instead as the diagram I posted shows. It was also used to kill a mag ignition if so equipped but that was more like the 2 digit numbered tractors (governor driven ignition not the 1/2 speed cam driven distributors) as I recall.

Take care Bob n behave out there now

PS those SM 2029 diagrams arent perfect so no warranty but my description above is how the 20 series operated. I KNOW I HAD MANY WHERE THE SAFETY WIRE WASNT THERE AND EVEN IF IGN OFF IF YOU STEPPED ON THE STARTER PEDAL THEY FIRED

John T

Yeppers, that wire (from switch to coil or low side of ballast) ADDS VOLTAGE while shes cranking, the ballast resistor limits current and reduces/drops voltage.

John T

John T
Yep I know I was thinking of 620 wiring instead 630 wiring such as your photo.

The statement: "This is the wire that limits the power to the coil." was made by Tom O. I just repeated it in a moment of silliness.

Yes, I have just had a lot of experience with just this problem. The tractor would start and just as you release the starter button it would stop. That third wire goes from the starter button to the top of the resistor and the bottom wire from the resistor goes to the coil. If the resistor fails it will not run unless you bypass the resistor. This setup is only on the 5, 6, and 730's gas tractors. Quite a common problem as I was told by local JD Dealer as he had a new resistor in stock.

Many thanks. You guys are great educators! Sorry about not including the wiring diagram in the original post--too late last night.

(quoted from post at 12:09:23 09/05/11) Yes, I have just had a lot of experience with just this problem. The tractor would start and just as you release the starter button it would stop. That third wire goes from the starter button to the top of the resistor and the bottom wire from the resistor goes to the coil. If the resistor fails it will not run unless you bypass the resistor. This setup is only on the 5, 6, and 730's gas tractors. Quite a common problem as I was told by local JD Dealer as he had a new resistor in stock.

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t was also on the LPG tractors. The problem I had was the starter button would not supply the 12v to the wire going to the resister. It you were very lucky, and the tractor was tuned just perfect it would sometimes start on the 6v only. But you couldn't count on it.

Oh My.. let me first start by saying that i'm new to this.. Bought my 58 720D last year. Pony runs like a champ. barely turns over before catching, one or so minute warm up add a little throttle engage the clutch and decompress. As soon as the oil pressure passes "L" release the decompress and we're running. Except when the pony"s starter solenoid won't pull in. Which was occurring about 25% of the time. So i decided to get rid on the 12v battery, fix the intermittent starting, and tidy up the wiring and get the gauges and lights working.. Put in 6 volt battery, removed the ballast resistor and hooked up generator. Pony started fine for awhile then started to act up. if i jumped the solenoid it would start right away. I replaced the solenoid. same thing Pony started fine for awhile then started to act up. To the heart of the matter. I pulled the instrument panel to start chasing wires and it is a mess. half the wires are missing or disconnected. the resistors for the lights and ignition appear good. I cleaned up all the wire connections and cleaned up the combination switch too. What I need is to find the proper start switch. it has a SPST in it. and I believe it needs a SPDT. also a good nickel tour on how the start and run circuits are supposed to work. I have the operator manual. service manual I&T book and the Parts Manual.

Thanks

Loren