[AT] tractor electrical question

Fri Aug 27 17:35:25 PDT 2021

I definitely think Carl is on to something.  I haven't studied the
schematic as he has.  But the main clue is that a jumper cures the
problem.  Keep it simple.  Whatever that jumper is jumping around is most
likely the problem.  Unfortunately there is another hypothesis.  It could
be a weakness somewhere (coil, let's say) that runs fine cold, but heats up
and starts to break down, but then... giving it a voltage boost gives it a
new lease on life.

SO

On Fri, Aug 27, 2021 at 4:52 PM Carl Szabelski <c.s.szabelski at gmail.com>
wrote:

> John,
>
> Found what I believe to be info on the starter relay and it appears there
> is no internal resistance, so back to square one (?). You indicated that
> with the wire removed from the R terminal you have 12V at the terminal.  If
> putting the wire back results in 6V at the coil, then that wire has to be
> what is causing the drop. There is a splice in the harness that splits the
> 12V in the harness. The part of the wire going to the coil may be high
> resistance wire. Have you tried bypassing that portion of the harness by
> running a wire from the R terminal to the coil with the original wire
> disconnected?
>
> Running out of ideas.
>
> Carl
>
> On Friday, August 27, 2021, Carl Szabelski <c.s.szabelski at gmail.com>
> wrote:
>
>> 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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>>> --
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>>>
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