Deere 955 Won't start - good battery and starter

[Enimo]

The PTO wasn't left on. I will test the neutral switch tomorrow after I recheck the starter and cables. I do not think the seat switch or PTO switch will keep it from starting, only will cut PTO off when you get off of seat, right?

 

[Enimo]

Thanks for the heads-up!

 

[Enimo]

Just to make sure...if I go from positive battery post to starter post the starter should spin. If it spins it isn't the starter but could be the solenoid so I can run from the positive battery post to where the small wire plugs into the solenoid and it should turn the starter, too, right? If it does it isn't the solenoid, it would have to be a ground or positive wire somewhere, the neutral switch, or the ignition switch, correct? Can I jump from the purple wire coming out of the switch straight to the solenoid to see if it is the ignition switch and/or the neutral switch?

 

[k0ua]

Do the voltage drop tests outlined by K7LN. Don't start doing all this starter removal, and things like that. If you took 100 "tractor wont start" cases, 99 out of 100 WOULD NOT BE ANYTHING TO DO WITH THE STARTER. The starter is the very LAST thing I would be concerned with. Starters RARELY ever are the problem. AND the fact that the lights go out when you turn the key, tells you IT IS NOT THE STARTER. Get a voltmeter, make the voltage drop tests, it will lead you to the culprit.

I always start with a voltmeter on the battery terminals themselves and have an assistant attempt to start the tractor. What happens? What is the reading before, and what is the reading while the key is turned to the start position and held there? What happens when you move out to the battery clamps on the terminals? Before and after? Move out to the tractor chassis for negative lead and starter main red post for positive lead. What happens, before and after. Then to determine if it is the positive battery cable or negative battery cable, make the voltage drop test across each end of the cable while the key is in the start position.

Battery cables/connections are about 75 percent of tractor no start problems. Followed by start relays, key switches, safety switches for the remaining 24 percent. and Starters/bendix MAYBE 1 percent. MAYBE. In your case the fact you noticed the lights (and I assume you mean headlights) go out, the battery cables or connections or battery is 100 percent the problem. Screwing around with a starter will NOT fix your tractor. A voltmeter and 2 to 3 minutes of measurements with an assistant WILL fix your tractor.

 

[zzvyb6]

Do the voltage drop tests outlined by K7LN. Don't start doing all this starter removal, and things like that. If you took 100 "tractor wont start" cases, 99 out of 100 WOULD NOT BE ANYTHING TO DO WITH THE STARTER. The starter is the very LAST thing I would be concerned with. Starters RARELY ever are the problem. AND the fact that the lights go out when you turn the key, tells you IT IS NOT THE STARTER. Get a voltmeter, make the voltage drop tests, it will lead you to the culprit.

Battery cables/connections are about 75 percent of tractor no start problems. Followed by start relays, key switches, safety switches for the remaining 24 percent. and Starters/bendix MAYBE 1 percent. MAYBE. In your case the fact you noticed the lights (and I assume you mean headlights) go out, the battery cables or connections or battery is 100 percent the problem. Screwing around with a starter will NOT fix your tractor. A voltmeter and 2 to 3 minutes of measurements with an assistant WILL fix your tractor.

All this seems pretty obvious, eh ? The key ingredients to this problem are: Brother in Law, seat forward and rain. Seat switch shorted by water + something else (Who peed on the seat near drain hole ?) Giant azz on the seat failed the seat switch ? PTO safety shorted closed, Neutral safety shorted closed. Left the lights on and the battery is almost dead ?

Maybe asking the BIL what really happened is the way to go. My JD gets lft out in the rain all the time. Drippage off the can-a-pee is the only problem I get from it.

"Neither a Borrower Nor a Lender Be."

 

[Kish318420]

So copper star washers won't conduct, gee I better pass that onto all electrical engineers and companies. :confused2:

 

[k0ua]

So copper star washers won't conduct, gee I better pass that onto all electrical engineers and companies. :confused2:

Again a lack of understanding of Ohm's law. The reason star washers are not generally used in high current applications is because added up all of the point contacts of the star washer are a small percentage of the contact that the normal terminal of the high current cable would have. Why does that matter? Because the small contact area will have more voltage drop E=IR. Do the math yourself. If the resistance is higher the drop will be more when the current is high. The purpose of a star washer is to prevent lossening of the fastener and possibly to "bite" thru paint. This is fine for lower current applications, but in high current applications this is not usually done. You need as much surface contact area as you can get to keep the resistance low.

To most people a wire is a wire is a wire. Not so. All wires are "shorted". They are a "dead short" hopefully, but they really arent. All wires and all connectors have resistance. Sure it is a small resistance, fractions of an Ohm. But resistance nonetheless. The larger the wire the less resistance. Have you ever thought about what is the difference between a #12 wire and a #00 wire? the #00 is quit a bit bigger than the #12 isn't it. So what? you ask. Well the #00 has much less resistance to current than the #12 and that mean when you want it to carry currents, like say 300 amperes, it is going to have much less voltage drop across a given length. So if you keep the current draw no more than 20 amperes, the #12 will serve fine as long as the length is kept short.

But to carry 300 amperes the #12 would act more like a fuse. So why would we want a star washer with the total point contact area adding up to about the cross sectional area of say a #12 in series with our current flow of 300 amperes? It wouldn't be a good idea. You may cinch down the star washer enough to crush it and gain some more surface area, but then the point of the reason for a star washer is somewhat negated.

So here is a thought experiment for you:. Say you stretch out a mile of telephone wire (a pair of wires) and say those wire are #24 gauge. And let put 12 volts DC across that pair of wires on one end and go to the other end 1 mile away and measure the voltage with a good hi impedence digital voltmeter. What will it measure? Well it will read 12 volts. How can that be? We have talked so much about voltage drops across wires, and now we have a very small cross sectional area wire and a very long length. Why doesn't the voltage drop? Why does it read the same at both ends? Again Ohm's law has the answer.

If you would like to learn more, just ask me!

 

[k0ua]

So what does my thought experiment have to do with the fact I may read 12 volts at the end of a "bad" battery cable just like I read 12 volts at the 1 mile end of my telephone wire. What I am trying to illustrate is you MUST have an understanding of Ohm's law to understand the relationship of Volts (Electomotive force the E in the equation) Current (the I in the equation in amperes) and Resistance (the R in the equation) E=IR.

A corroded battery cable will still read 12 volts at the end UNTIL you try to draw current thru the cable. And it will likely have a low voltage drop as long as the current is kept to a modest amount. Sure there is resistance in the cable but if the current demand is kept low (lights instruments, etc) the voltage drop will be low. But if the current demand is high (spinning a starter against a cold engine) then the voltage drop will be high.

Now go to the end of your mile of telephone wire #24 gauge that you measured 12 volts on and try to even light a tail light bulb. About a 2 ampere load. Try it and see what happens. Measure the voltage now. The voltage will have dropped to near zero. Why? Again E=IR has the answer.

These are the points I am trying to make with all of this. To fix your tractor, you need Ohm's law. AND it is not just a good idea, it IS the law!

So that 9th grade algebra was useful after all, wasn't it?

 

[beenthere]

k0ua
A very good descriptive lesson and thanks for the time you took to explain it. Happy 4th

 

[Kish318420]

You might want to google using this "best practice use of copper star washers in electrical circuits"

Lots of PDF white papers on using proper ways for connections in high voltage and high current circuits. I'll go with experienced journeyman electricians and electrical engineers.