[AT] tractor electrical question

Thu Aug 26 12:39:17 PDT 2021

I just realized I misspoke previously. I was looking at the diagram where
it calls out the “cranking motor” and should have realized that the diagram
is actually showing the connections to the starter coil. So your issue may
be with the starter coil, not the starter itself. Don’t know if you can
open up the starter coil to get a look inside at the contacts, on some you
can. Try totally removing the starter coil and reinstalling it, making sure
all connections are good and you have a good ground. And if you can get at
the internals of the starter coil, try cleaning all the contact points.

Another check you can do first is similar to what you did with running a
wire directly to the ignition coil from the battery. This time jumper from
the battery connection at the starter relay to the terminal on the starter
relay that goes to the coil. If the engine runs like it should then the
only thing that is no longer in the circuit is the starter relay, and it
has to be the culprit.

Carl

On Thursday, August 26, 2021, Carl Szabelski <c.s.szabelski at gmail.com>
wrote:

>  By the way, I believe it’s not the coil and is related to the cranking
> motor. Especially since the voltage drops when you bump it like you said.
> Something in the motor may be partially shorted or corroded, causing a
> voltage drop to the coil. The coil should always see 12V whether or not
> there is a resistor, internal or external. The resistor is essentially
> after the coil winding and drops the voltage after the winding, not before
> it. If the engine is running fine when you directly connect 12V to the
> coil, the coil is working like it should and is good.
>
> Carl
>
> On Thursday, August 26, 2021, Howard Pletcher <hrpletch at gmail.com> wrote:
>
>> I would concentrate on the coil first.  Defective new ones are not
>> unheard of.  Have you got another vehicle--tractor or car or truck--that
>> you could swap with. Any that has 6V to the coil when running should work.
>> If it won't fit your mounting, just secure it temporarily, be sure the case
>> is well grounded, and see what happens as it runs for a time.  And you can
>> test the one from the tractor in the donor vehicle.
>>
>> Howard
>>
>> On Wed, Aug 25, 2021 at 11:54 PM John Hall <jtchall at nc.rr.com> wrote:
>>
>>> Ordered coil from CaseIH by the parts book is all I know. I have the
>>> same issue with either coil. After reading about ignition systems, it seems
>>> resistors are used in a different circuit for once engine is running,
>>> voltage is dropped so as not to burn points. 12 volts are sent for cranking
>>> only. I'm wondering if there is a resistor somewhere thats failing when it
>>> gets hot?
>>>
>>> John Hall
>>>
>>>
>>>
>>> On 8/25/2021 11:21 PM, Howard Pletcher wrote:
>>>
>>> Is that the original coil?
>>>
>>> I'm not familiar with the 454, but in the truck world, most coils are
>>> intended for 6V use.  There is a resistor wire in the harness that drops
>>> the voltage while the current is flowing with the points closed.  But there
>>> are also coils intended for 12V use with no resistor wire.  If that is not
>>> the original coil, perhaps you have the wrong one.
>>>
>>> Since it seems to work fine with 12V applied, I'd probably run another
>>> wire from the ignition switch to the coil to bypass any possible resistor
>>> wire.
>>>
>>> Howard
>>>
>>> On Wed, Aug 25, 2021 at 11:08 PM John Hall <jtchall at nc.rr.com> wrote:
>>>
>>>>
>>>> If there is, I can't find it. Closes thing I have found is the
>>>> diode/rectifier for the alternator. Its inline and is tied in on this
>>>> particular "circuit" . Matter of fact, the side opposite the alternator
>>>> is where the fuel solenoid feeds from.
>>>>
>>>> John Hall
>>>>
>>>>
>>>> On 8/25/2021 11:05 PM, Spencer Yost wrote:
>>>> > Maybe there’s an external resistor?
>>>> >
>>>> > Spencer
>>>> >
>>>> > Sent from my iPhone
>>>> >
>>>> >> On Aug 25, 2021, at 10:35 PM, John Hall <jtchall at nc.rr.com> wrote:
>>>> >>
>>>> >> Got what I hope is a simple question. On my IH 454 tractor, is the
>>>> voltage going to the coil a constant 12V? I'm having some issues with it
>>>> running bad when it gets hot (I've already replaced everything but the plug
>>>> wires). Found out today that if I run a jumper wire from battery to the
>>>> coil, the problem goes away. Take it off problem comes back, put it back it
>>>> goes away, take it off, it comes back. So I am tracing the wiring but this
>>>> one isn't simple, new enough there are tons of gauges, fuel solenoids,
>>>> safety switches, etc. Anyway, if I check voltage at the coil, the fuel
>>>> solenoid, and there is one small terminal on starter solenoid that all read
>>>> 12V if the switch is on. If I bump the engine over slightly (I guess the
>>>> pts are closing) then the coil and starter drop to just under 6V, fuel
>>>> solenoid stays the same. So shouldn't there always be 12V at the coil?
>>>> >>
>>>> >> John Hall
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>>>
>>>
>>> --
>>> Howard
>>>
>>> _______________________________________________
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>>
>>
>> --
>> Howard
>>
>
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