[AT] tractor electrical question
John Hall
jtchall at nc.rr.com
Thu Aug 26 19:54:57 PDT 2021
No PO, we bought it new. Put a new harness on 20-25 years ago--its in
good condition and we haven't hacked into it anywhere.
6 or 12 volts to the coil (depending on if the pts are open/closed)
except when cranking, then it maintains 12. It is my understanding the
starter solenoid is what provides the boost in Voltage when the starter
is engaged--I verified it is outputting 12 volts when starter engaged
and I had the wire disconnected from solenoid--this is on the R terminal.
The new coil is marked 12V, nothing else, yet the description on the
bill was for 6 volt. It was in an unopened CaseIh box. Part number on
the box and online manuals matches my 50 year old paper parts
book--thats encouraging. Trying to cross over the CaseIH part # to see
exactly what it calls for doesn't really work too well, I kept getting
different answers, thats why I ordered one from the dealer--not saying
its right, but figured OEM would be the simplest.
The old coil was probably on there for 15+ years--it only had one wire
to the + terminal. IH schematic shows 1 wire as well.
I've looked for an external resistor and so far have found nothing.
Researching online suggests ignition systems using resistor wire--I have
no idea about such.
I'm willing to go get a coil from the parts house or rob one off a
lawnmower for testing. I just need this thing fixed ASAP as I don't have
another tractor to do what it does--and my time needs to be spent on
other things. Bad how this stuff never happens in the off season when
time is on your side!!
John Hall
On 8/26/2021 10:27 PM, Carl Szabelski wrote:
> If you’re reading 6V at the coil on a 12V system with the engine off
> and the ignition switch in the on position, then you’re dropping 6V
> from the starter relay to the coil. That would indicate you have a
> ballasted ignition system which has a ballast resistor in the wire
> going from the relay to the coil. There should be a second wire
> attached to the + terminal of the coil that provides 12V during a
> start by temporarily bypassing the ballast resistor through the
> ignition switch when you start. The reason the new coil is marked 6V
> is because that’s what you need. The coil should only need 6V when the
> engine is running. Running at 12V will cause the coil to overheat and
> eventually fail. Applying 12V during a start for a short time doesn’t
> hurt it.
>
> If you don’t have the second wire, then you probably have a coil with
> an internal resistor. That requires 12V to the coil at all times, 6V
> will be dropped internally through the internal resistor. Maybe the PO
> did some rewiring and left a ballast resistor in while putting in a
> coil with an internal resistor. If you do have an in-line ballast
> resistor and a coil with an internal resistor, then you have too much
> resistance and you’re dropping too much current going through the
> coil, which gives you a weaker spark. That may be why putting 12V
> directly to the coil makes it run better. You’re overcoming the extra
> resistance with twice the voltage.
>
> The first thing you need to do is determine which type of system you
> have (ballasted or non-ballasted), and if you have the right coil
> (internal resistor or not). From looking at the wiring diagram I sent
> earlier it doesn’t seem to indicate you should have a ballasted system
> since it doesn’t show a second wire at the coil. But again, maybe the
> PO made some modifications?
>
> Now if you’re dropping 6V at the starter relay, then the relay or the
> connection to the relay is suspect. That’s why I suggested testing the
> starter relay to see if you were dropping voltage there.
>
> Once you have a definite idea of what type of system you have, it
> should make finding the problem easier.
>
> Carl
>
> On Thursday, August 26, 2021, John Hall <jtchall at nc.rr.com
> <mailto:jtchall at nc.rr.com>> wrote:
>
> points, plugs, cap, rotor and coil are all new. I verified with my
> 50 year old parts book and it has the same part# for coil as what
> online parts at Case is showing. The new coil has 12V on the
> outside, but the bill had 6V. Box was sealed up, but it came from
> overseas, so a lot of variables there
>
> Point gap was verified when I had the distributor off and plate
> out so I could make sure weights were free and springs not broken.
>
> I had my voltage regulator with me yesterday. When I tried to
> check at coil with engine running rough, it showed OL for whatever
> reason. I've checked so much stuff lately that I'm not sure but I
> think I got 6 and 12 volt readings depending on where the points
> were once I shut the engine off. I tried checking the voltage with
> engine running at the fuel solenoid for reference and it was
> floating all over the place from 4 to 13.5V. This was observed
> with the engine hot and running rough. With engine not running it
> holds steady a little over 12.
>
> Last night I also found that the wire to the coil and the wire to
> the R terminal on starter solenoid can read 6V (little less
> actually) while the wire going to the fuel solenoid in the carb
> was reading 12V.
>
> John Hall
>
>
>
> On 8/26/2021 6:35 PM, Howard Pletcher wrote:
>> It's not unheard of, particularly since many of those parts now
>> come from overseas. To me, swapping with another if you can find
>> something to swap with would be the easiest way to prove or
>> eliminate that as a possibility.
>>
>> Make sure your points setting is close to spec and they are clean
>> as that would affect the ignition. Have you looked at your
>> plugs, not thinking that's the problem, but if they are fouled or
>> badly gapped, they could have an effect. You also might run it
>> until it heats up and needs the 12V to see if it still shows 6V
>> to the coil. If not, then it's somewhere else in the circuit.
>>
>> Many of the other things suggested have no connection with the
>> ignition circuit.
>>
>> On Thu, Aug 26, 2021 at 5:12 PM John Hall <jtchall at nc.rr.com
>> <mailto:jtchall at nc.rr.com>> wrote:
>>
>> Howard, you are leaning toward new coil and old coil are both
>> bad?
>>
>> John Hall
>>
>> On 8/26/2021 3:47 PM, Howard Pletcher wrote:
>>> No, what he is reporting is just what should be happening.
>>> With the points open, no current is flowing through the
>>> primary circuit and there is 12V at the + side of the coil.
>>> When he bumped the starter and closed the points, the
>>> current flowing through the resistor in the primary circuit
>>> results in a voltage drop so that there is now 6V on the
>>> coil as intended.
>>>
>>> The wire from the starter to the coil does send 12V directly
>>> to the coil, but this is only engaged while the starter is
>>> cranking in order to produce a hotter spark for starting and
>>> is not connected to 12V the rest of the time.
>>>
>>> The fact the coil seems to require 12V to its terminal when
>>> hot points to an internal problem in the coil as discussed
>>> by Dell in the Yesterday's Tractors article.
>>>
>>> Howard
>>>
>>>
>>>
>>> On Thu, Aug 26, 2021 at 2:53 PM Carl Szabelski
>>> <c.s.szabelski at gmail.com <mailto: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
>>>
>>>
>>>
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>> --
>> Howard
>>
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