[AT] tractor electrical question

Fri Aug 27 18:21:01 PDT 2021

On the 1960's Ford vehicles (and others, I'm sure) they had a wire in the
harness that was specifically resistive which seems to match some of the
descriptions given. If wire has 12V on one end and 6V on the other end
going into the coil, it's like having the resistor inline. The vehicles had
a wire from the solenoid to the coil that would bypass the resistive
element in the harness by going straight to the battery for starting
purposes, giving full battery voltage (albeit drawn down by the starter) to
make the spark hotter (since the battery voltage would drop severely during
cranking it made starting hard). The coils were set up to run on 6-8 volts
to make this work. If this is the same in your tractor application it could
be part of what you're seeing. These wires are generally nichrome wire and
have a few ohms to them (should be enough to measure on a DVM if
disconnected from the rest of the circuit; it should be similar to a
resistor inline as it does the same function). Nichrome wire is pretty
resilient to aging but connecting to it (with perhaps a crimp connector or
something like that) could be a problem over time.
   Since you're able to get the thing to work correctly with a jumper from
the battery it seems there is resistance somewhere. I think you mentioned
having 12V at the switch but 6V at the coil when sitting still and the
points closed. That sounds like a resistive wire in the harness. My
thinking would be to run a new wire from the switch, through a regular
ballast resistor and to the coil to bypass the potentially bad resistive
wire in the harness (it may be heating up and the connections giving you
fits).

Just my $0.02 but those pink Ford wires hosed a lot of folks over the
years.... :)

Ken in AZ

On Fri, Aug 27, 2021 at 5:36 PM Stephen Offiler <soffiler at gmail.com> wrote:

> 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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>>>>
>>>>
>>>> --
>>>> Howard
>>>>
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