[AT] tractor electrical question

Fri Aug 27 12:52:46 PDT 2021

John, I’ve gone trough the wiring diagram and traced all the feeds from the
R terminal on the starter relay, one of course goes to the coil. All the
other feeds go to things like sensors, the fuel shutoff valve, etc. They
all form parallel circuits to the coil, eventually going to ground. If
there was a short anywhere it would take the R terminal to ground and you
wouldn’t see any voltage at the coil, or possibly anywhere else.

I’m still of the mind that your issue is with the starter relay. I don’t
know the internals of the relay, but from how I believe it should work is
that the relay has an internal resistance built into it to drop the voltage
to 6V after the start. During a start the resistance is bypassed and you
get 12V at the coil, necessary for cold weather starts. This is all done
with two sets of contacts built into the relay. What I think is happening
is the contacts for the internal resistance are remaining closed after the
start, thereby leaving that resistance in the circuit. That along with any
internal resistor in the coil is too much resistance at 6V for the coil to
work properly. The contacts are probably shut closed after years of arcing.

One thing to try is hitting the relay to see if you can break the contacts
free, assuming they are there. Also as I mentioned earlier, see if you can
open up the relay and look inside.

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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