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New Holland TC-40 tractor fuse blows on turning key to start position

Customer Question
I have a New Holland...

I have a New Holland TC-40 tractor. When I try to start it, the 7.5 amp fuse blows as soon as the key is turned to the start position. I can't find what is causing the problem. What do I do.
I have previously dealt with JD. Loechelt .

Submitted: 8 years ago.Category: Heavy Equipment
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Answered in 21 hours by:
7/2/2009
Technician: Matthias, Technician replied 8 years ago
Matthias
Matthias, Technician
Category: Heavy Equipment
Satisfied Customers: 114
Experience: 10+ Yrs experience in Heavy Duty / Automotive / John Deere,New Holland and Case IH, Cummins and Cat
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Hello there

What label does that fuse have?

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Customer reply replied 8 years ago
The box is labeled ATO 7.5. The fuse that burned out had been in for about a year. The ones I put in after it burned out were from the same box.
Technician: Matthias, Technician replied 8 years ago

Sorry, I should have been a bit more clear, what circuit is the fuse protecting?

There should be a legend in the user manual.

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Customer reply replied 8 years ago
To me the wiring diagrams are about as clear as mud. There are seven fuses in the fuse panel. There are three that are 7.5 amp. The one that blows is the second from the left. Turning the switch to the on position lights up the glow plug light on the dash, but does not affect the fuse. Turning the key to the start position blows the fuse.
It appears to me as though the particular fuse is either F1 or F2. I cannot determine which based on the schematic I have. Perhaps you know enough about the system to ask me another question that will clarify it.
Technician: Matthias, Technician replied 8 years ago

Hello there,

Sorry for the late reply.

I am pretty sure the fuse that blows is for the start circuit.

Disconnect the small wires from the starter and make sure they do not touch any metal to cause a short.

try the key switch in start position and see if the fuse blows, if it doesn't the starter solenoid is the problem

Let me know what you find

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Customer reply replied 8 years ago

I am assuming that "the small wires" is the single white wire that connects to the bottom of the starter. Is that correct?

Technician: Matthias, Technician replied 8 years ago
yep, sometimes there are 2, so disconnect that one and let me know what you find
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Customer reply replied 8 years ago
I disconnected the white wire, put in a new fuse, turned the key to the on position where the dash lights including the glow plug light came on, then turned the key to the start position. Nothing happened.
Technician: Matthias, Technician replied 8 years ago

Good, so as soon as the starter is disconnected the fuse doesn't blow.

Take the started off the tractor and take it to your New Holland dealer, he should be able to check it out and repair if possible

Good luck

Matthias
Matthias, Technician
Category: Heavy Equipment
Satisfied Customers: 114
Experience: 10+ Yrs experience in Heavy Duty / Automotive / John Deere,New Holland and Case IH, Cummins and Cat
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Customer reply replied 8 years ago
I wanted to determine if it was the starter or the solenoid. I connected the positive lead of the VOM to the white wire and grounded the other lead to the tractor frame (using vice grips). I then turned the key to the on position, and read about .08 volts. I then turned the key to the start position and read 0.17 volts. I then used the VOM to measure the voltage at the battery, using the same setting, and got 12.43 volts.
What did I learn?
Technician: Matthias, Technician replied 8 years ago

Sorry about that,

Did you press the clutch pedal?

Or is the transmission in neutral?

Because the results you are getting point to a faulty start switch or circuit

Let me know what you find

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Customer reply replied 8 years ago
I screwed up yesterday, I did not have it in neutral. So today I did.
New results- positive lead from the VOM to the white wire, negative lead with good ground, key turned to start position: result was 10.8 volts.
I then checked the voltage at the main wire from the battery, that measured 12.6 volts. I was under the impression that I should have gotten 12 volts at the white wire when the key was in the start position. Is that not correct?
Again, the fuse did not blow during this test.
Technician: Matthias, Technician replied 8 years ago

No problem,

Thats not to bad, the power from the switch is only a signal that goes through all the safety switches to engage the big solenoid on the starter.

Try to jump the starter by jumping a wire from the big terminal on the starter to where the white wire was hooked up.

don't turn the key to the run position when you do this so that the engine can't start but just turns over.

If nothing happens but a big spark, the starter solenoid or starter is defective.

Becarefull and make sure the transmission is in neutral

Let me know what happens.

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Customer reply replied 8 years ago
I jumped a connection between where the white wire was hooked to the big terminal. The key was off, transmission in neutral. The starter engaged and spun the engine.
Technician: Matthias, Technician replied 8 years ago

Hmmm, was there a big spark?

the solenoid might draw to many amps, does your multi meter have a amperage setting?

If it does it needs to be 20 A minimum. put the multimeter in series with the terminal where the white wire hooks up and engage the starter again and see how many amps the starter solenoid takes.

If a starter gets a dirty/dusty bendix (drive gear on the end) it takes more power from the solenoid to slide the gear over to engage in the flywheel

I would take it off and see if you can clean it, dry everything and see if it moves freely.

Let me know what you find

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Customer reply replied 8 years ago
There was a spark, but not a big one by any means.
My VOM does have an amp setting. Will it damage the VOM if I run all of that current through it? Seems like a lot to put through my little instument. I'm assuming it will get 12 volts with the full load of the battery, is that correct?
I am also assuming that test should be done before I remove the starter from the tractor.
Technician: Matthias, Technician replied 8 years ago

yep, the test should be done before the starter is removed

If the 7.5 amp fuse blows there will flowing more amps through the meter.

But only the amount needed to engage the solenoid not the current needed to turn over the engine.

Most meters can handle 20 A and have an internal fuse to protect the meter.

I am guessing you will be seeing about 10 - 15 amps.

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Customer reply replied 8 years ago
My VOM can handle 200ma, so that won't work. I have taken the starter off, It is hard to turn by hand, but everything is clean. I will take it into town Monday, can't do anything until then.
Technician: Matthias, Technician replied 8 years ago
Ok, we will see what they find
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Customer reply replied 8 years ago
Took the starter in to the NAPA auto parts store and had them test it. The said that the starter and the solenoid are both fine.
The fellow there thought the 10.8 volts measured at the white wire when the key was in the start position was too low, and indicated a short somewhere. What do you think? What do I do now?
Technician: Matthias, Technician replied 8 years ago

Hello there,

If there is a short in the wiring, the fuse would blow even with the starter disconnected and the key in start position. You try to follow the white wire and see if there is a bad connection down the line.

If there was a short there would be no power at all when the key is in start position.

Check the harness and see if you see any bad or corroded connections

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Customer reply replied 8 years ago
I cannot find anything wrong with the wiring. It is difficult to try to trace wires because the numbers on the wires shown in the operators manual are different than the numbers on the wires on the tractor.
I'm wondering if it could be related to the so-called "safety" switches. I know there is one under the seat, at the PTO lever, and in the transmission. Are there others? What if I just shunt all of them?
Technician: Matthias, Technician replied 8 years ago

All those switches are in series in the start circuit. some switches have more then 2 wires.

You can Jump the switches with 2 wires one by one while checking the voltage at the white wire at the starter. If the voltage goes up to battery voltage, you have found the 'weak' switch.

It is still weird how it started with a blown fuse

For your information:

If the voltage drops the required amperage goes up, but it shouldn't blow the 7.5 amp fuse

12v at 7.5 amps = 90 watts so 10.8v producing 90 watts draws only 8.33 amps

That little jump shouldn't blow the fuse. assuming the fuse is there to protect the circuit so the normal amperage is well below 7.5

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Customer reply replied 8 years ago
Reinstalled the starter, hooked everything up except the white wire. Connected the VOM to the white wire as before (positive to white wire, negative to frame), turned the key to the start position and recorded 11.1 volts. Connected the white wire to starter, turned key to start position, starter turned, engine started, fuse did not blow. Please tell me something is "fixed", and that it won't fail again next time I want to start it. Why did it start this time?
Technician: Matthias, Technician replied 8 years ago

weird,

Looks like there where 2 problems, and they got magicly fixed.

There might be a wire thats bare and almost worn through, it maybee grounded once in a while. and now because of you moving the harness arround its not touching any bare metal. I would keep an eye on it and leave it the way it is.

I am still wondering how many amps the solenoid on the starter draws.

It might work fine on the test bench, but they do not check for current draw on solenoid

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Customer reply replied 8 years ago
I started the tractor today, ran it for about 1/2 hour then shut if off and started it again. Wanted to see that it worked when hot, since that was the case when it first failed. Then worked it about 3 hours, shut it off and then restarted it again. It has to go into some areas where I cannot tow it out if it won't start, so I am concerned.
My son is coming over next week and has a meter that we can use to measure the amperage in the white wire.
I still don't have a clue as to why it failed, or what fixed it, but thanks for the help anyway.
Technician: Matthias, Technician replied 8 years ago

Thanks for accepting my answers

Its is weird, but keep me posted

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Customer reply replied 8 years ago
We have to start again.
I don't know how to put in a new deposit, let me know.
I have been informed (second hand) that the problem may be the fuel shut off solenoid, and that I need to check the resistance at it. I don't know where it is or what it looks like. Can you help me identify it?
Technician: Matthias, Technician replied 8 years ago

No problem, don't worry about paying

The fuel shut off solenoid receives power in the run and start position.

But if you want you can check it, Locate the Injection pump, there solenoid looks like a small barrel and there should be a couple or just one wire attached to it.

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Customer reply replied 8 years ago
OK, I found it (behind the loader arms and hose connections). The word was to check it for resistance. How do I do that? Do I unplug the wire that goes into it, then put the red wire on that connection and the other wire on the battery post?
Technician: Matthias, Technician replied 8 years ago

Hi,

Unplug the wire that hooks up to it,

Set you multi meter to Ohm and check between the 'hookup' and a good ground on engine.

But if you engine starts and runs the fuel solenoid is Ok, I have not seen many fail. other then in severe heat and vibrations

I couldn't tell you the right value

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Category: Heavy Equipment
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