# 720 electrical issue



## tkwoof (Feb 27, 2006)

Howdy,
I have a John Deere 720 that is acting up. when you turn the ignition switch the gauges don't move anymore and the lights don't come, that is until you press the starter button then they all come on. The tractor will crank and run but as soon you release the switch it shuts off. Any Ideas?
I am thinking it is the regulator but this is my first JD so I thought I would ask first.

thanks


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## Chris (Sep 15, 2003)

Welcome tkwoof! 

I am sure the JD experts will chime in soon! Thanks for stopping in and hope you enjoy TF!

Cheers,
Andy


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## Live Oak (Dec 22, 2003)

I am thinking you may have a poor or corroded battery connection either at the battery terminals or at the frame or starter connection. I believe there is a starter or voltage relay in this system and it sounds like it may be a good place to look at as it appears that it lets voltage through while you make start attempts but does not when you release the starter button. Do you have a repair manual or something that shows the wire diagram of the electrical system?


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## Live Oak (Dec 22, 2003)

Welcome to Tractor Forum by the way tkwoof! Is this 720 a workin' tractor?


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## tkwoof (Feb 27, 2006)

*More info*

Thanks for the quick replies.
I do have the original manual and an I&T manual for this thactor but there is no wiring diagram in either. This is a working tractor. I purchased a house and it came with a JD 70 and 720.
the 70 is a diesel I haven't really looked at it yet. the 720 was the closest tractor to the shed door so I figured it would be a good place to start since it would block the exit if I got the other one running first. 

A little additional info. I was working on the tractor and replaced the battery with a new 70/700 automotive battery (the tractor is on a 12v system) I ran the battery dead because the carb was gummed up, so removed the carb and rebuilt it. I put the carb back on and tried to start the tractor, at this time when turned the console switch the gauges would move and the lights would come on, with the battery being dead I hooked up my battery charger/starter and switched it to 200 AMP start and attempted to start the tractor it sputtered a couple of times and I heard the battery boil so I shut off the charger. after a few minutes I went back and switched the charger back on to 200 AMP and when I turned the console switch the gauges would no longer move and the lights would come on only when the starter button was engaged. It cranked and would run only while the starter button was pressed.

thanks again


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## tkwoof (Feb 27, 2006)

*More info*

.


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## Live Oak (Dec 22, 2003)

Follow the positive cable off of the battery back and see if it doesn't connect to a relay of some sort. I bet your dash panel gets its voltage from this relay or one further on down the line. I am not real familiar with the 720. That tractor is as old or older than I am.   But still a real nice machine. You battery charger pushing that much through the system may have damaged the relay. Or at least the side of the relay that provides power to your dash panel display. You may have blown an inline fuse or something similar. You will have to start at the beginning (battery) and work your way back tracing wires and testing connections for voltage and that they are clean.


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## tkwoof (Feb 27, 2006)

*final Note*

Thanks Chief,

I also noticed that the battery I removed (and the one I put in its' place) has + to chasis and - to the starter, I thought this was odd but what do I know.


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## Chris (Sep 15, 2003)

Is that a narrow or wide front 720? Diesel or LP? From what I recall on these tractors, they even had an optional 24V system available...You know the funny thing is that the 720 is the direct replacement for the 70. Guess the owner just upgraded when the time came around for a new tractor. Lots of improvements on the 720. 

Love those old tractors! Looks great restored! Where do you call home, TK?

<img width=600 height=480 src=http://www.tractorforum.com/JD720.jpg>


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## Archdean (Jul 15, 2004)

"I heard the Battery boil"

Strongly suggests a poliarity problem!!

A JD dealer in your area will have a schematic of your tractor! certainly worth a phone call!!

Good luck!


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## tkwoof (Feb 27, 2006)

*figured it out*

I found a blown fuse in line with the switch, it was covered with a mound of 10 year electrical tape. I removed the fuse and wired it direct to test it and it worked. so that's one problem down. Oh and to answer your question admin it's a wide front gas 720. and we live in Michigan.

Next issue ... fix one problem 2 take their place right?

I cleaned up the carb and removed about an inch of sludge from the bowl put it all back together and adjusted the float valve all the way down. that was last night I went out to the barn this morning and the ground under the tractor was soaked with fuel. I thought at first the carb was leaking, so I tightened everything down to be sure. I walked around the tractor to the side with the exhaust pipe and saw gas dripping from the exhaust. I removed the spark plugs and cycled the engine a couple of times and it shot fuel out 20 ft on both sides of the tractor. It filled the engine with about 5 gallons of gas.... any ideas what could be out of adjustment here? is it possible that adjusting the float valve did this? 

thanks again


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## Live Oak (Dec 22, 2003)

You should have left the float valve adustment alone if it was working before. In adjusting the float valve all the way down; it appears that the float was able to reach its max. level and still not turn the fuel off. Or a few other possible scenarios to consider................. #1 the fuel bowl float has a hole or crack in it and has filled with gas and will not shut the fuel off.............. #2 the float valve is stuck in the open position. The reason the engine fill with gas and the carb made such a mess is that if the fuel bowl float valve does not shut off the fuel; it will continue to flow into the fuel bowl and leak out of the fuel bowl vent in the carb. throat. You were very wise to remove the spark plugs and check as you could have bent a rod or damaged something in the engine if the starter was real strong. Once you identify and repair the problem with the carb. be sure to change the oil and filter if any and try the engine out again. 

On these old machines it is best not to adjust anything if it was working right before. Get it running first and then make the adjustments to improve things in small increments.


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## tkwoof (Feb 27, 2006)

Gotcha,
I should have readjusted the valve to what it was prior to cleaning. the whole carb was gummed up pretty bad. It sat for about a year with a little gas in the tank and the fuel line. I am letting it dry out now and will change the oil and filters (that was my next question) before I run it.

Thanks again Chief


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## tkwoof (Feb 27, 2006)

*Spoke to JD Dealer*

Just got back from the JD Dealer and they were full of info.
the 720 is + to chasis so that was right
the reason the engine filled with fuel was according to them the bladder that rests on top of the sediment cup. they said that what can happen is that they get old and allow the fuel to continuously flow to the engine...
I still think it was a misset float but to be safe I purchased a new set of bladders. I also got a wiring diagram and parts breakdown from them. Thanks again for all of your assistance I will let you know how it goes.


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## DEERE180 (Jun 20, 2006)

Having a "heard the battery boil" when one attaches a 200Amp starter-charger will make just about any battery boil. As I understand it some of the older tractor used to be positive ground (just like some of the older cars).

May I suggest that you verify the starter switch. It may be a double pole double throw and it may not be going back to the proper setting, thereby not allowing juice to flow to the instrument cluster.

Take a VOM and check out the voltages and the proper operation of the switch(es) including the starter swtich.


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