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<p>Hi Dean,</p>
<p>Working from your last question first. Do you need the wire from
the solenoid to the coil?</p>
<p>That would depend on your ignition switch. IF the run wire is hot
while in the START position, then no you don't need the secondary
wire. Most ignition switches do not power the RUN wire while in
the START position. There are several reasons for this with the
most important being to reduce any extra load on the battery
during start and to prevent reverse spikes from the starter back
into any of the other electrical system. <br>
</p>
<p>This is easy enough to test. Remove both wires from the coil +
terminal and put a test light on the one from the switch. Turn key
to RUN, light should come on. Turn key to START, light should go
out. If it stays on, you don't need the wire from the solenoid. My
bet is it will go out, and you need the wire from the solenoid.</p>
<p>Next up was the do I need a resistance with the 12V coil? The
short answer is maybe. I am a little surprised that the factory
used a "resistance wire" on the 6V setup, but again, that was to
protect the points primarily and the coil from overheating.
Resistance wire is an older way of dealing with the points than a
resistance block. The problem with resistance wire is it comes in
many different amounts of ohms of resistance per length of wire.
So you need to know the total amount of resistance required, then
cut the appropriate length of wire to get that amount. Wire
diameter also plays a part depending on how much current that wire
was expected to carry. I think the use of resistance wire was
eventually replaced by resistor blocks.</p>
<p>Now we get into the question of 12V coils and this is where I get
a little bit fuzzy both from lack of total knowledge of the
subject and fading memory from when I was a parts guy in the
1980's. IF I remember correctly, Ford and GM used a different coil
that did not require an external resistor. Did it have an internal
one? I don't know but I do remember looking up coils for vehicles
and there would be different part number for "with resistor" and
"without resistor". This may have been as Chrysler was changing to
a system that did not require a resistor. Another fuzzy memory is
some coils were grounded through the mounting strap and only had
one + terminal, some had a + and - terminal and were not grounded
through the body. <br>
</p>
<p>There may be writing on the coil that says if it needs a resistor
or not. Or if there is a brand name and part number, it could be
researched that way.</p>
<p>In any case, since it has been working fine with no burned points
issues, my instinct would be to leave it alone and just replace
the damaged wire. If it ain't broke, don't fix it. :)</p>
<p>All coils cause a reverse spike on the primary winding as the
magnetic field of the secondary winding collapses. This is why
points can arc and why there is a condenser connected to the
points. A coil designed for 6V will work at 12 and will produce a
hotter spark. The stress on the coil and condenser as well as the
heat buildup in the coil will eventually damage it. If one is
converting a 6V system to 12V everything will work fine as long as
the coil and condenser are upgraded to 12V versions OR some
provision is made to reduce the voltage to the old coil. IF the 6V
system also used a reducing resistance it makes things more
complicated and switching everything to 12V is just easier all the
way around.</p>
<p>If you are curious, just do the test light procedure and you will
find out how it is set up now. The big question will be how to
keep the darned mice from doing it again! <br>
</p>
<p>Stuart<br>
</p>
<div class="moz-cite-prefix">On 8/31/24 10:59, Dean Vinson wrote:<br>
</div>
<blockquote type="cite"
cite="mid:000001dafbbe$cc6acbc0$65406340$@vinsonfarm.net">
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<p class="MsoNormal">Stuart and Dean, thanks for the quick
responses. I’ll go ahead and put a new length of wire in
there to replace the one that had some of the insulation
chewed off, on the theory that whoever installed the old one
knew what they were doing and in light of the fact that it’s
evidently been installed for a long time and the tractor runs
fine. But I still don’t really have a good understanding of
the whole system as currently configured… my technical
foundation is a little weak for stuff like this.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Stuart, you wrote “The purpose was not to
protect the coil but to protect the points”, and Dean, you
wrote “Starts on 12v runs on 6.” Ah, okay—so that’s why
there are two wires feeding the coil? One from the starter
solenoid to briefly provide 12V to the coil to generate an
especially hot spark for starting, and then after the solenoid
disengages the separate “resistance” wire from the ignition
switch provides reduced voltage to avoid burning out the
points while the engine is running normally?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m familiar with the resistors in the
little ceramic blocks, since my Super M has one, but it’s an
after-market add-on since that tractor left the factory with a
6V battery and was at some point converted to 12V. Following
the same logic, it’d make sense to me if the 3020 had a
physical resistor in front of the coil, since they were
designed from the get-go for 12V batteries but still used 6V
coils. But the service manual wiring diagrams don’t show any
resistor, just a “resistance wire,” and this little four-foot
section of #14 stranded wire doesn’t provide any resistance to
speak of.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Oh, wait… okay, maybe that makes sense
after all, because I think this four-foot wire is not OEM and
I think the coil on the tractor is not the OEM 6V coil but is
rather a 12V replacement. A 12V coil wouldn’t need a
resistor to avoid burning the points, correct? So 12V to the
coil is okay all the time and I don’t *<b>need</b>* a
resistor, but I need that 12V to come from the ignition
circuit since the 12V from the starter solenoid is only there
when starting. Sound right? And if so, do I strictly need
the wire from the solenoid? (Not that I’m intending to
remove it… just trying to think through how the system works
as currently configured).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks very much,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dean Vinson<o:p></o:p></p>
<p class="MsoNormal">Saint Paris, Ohio<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div
style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="mso-ligatures:none">From:</span></b><span
style="mso-ligatures:none"> AT
<a class="moz-txt-link-rfc2396E" href="mailto:at-bounces@lists.antique-tractor.com"><at-bounces@lists.antique-tractor.com></a> <b>On
Behalf Of </b>Stuart Harner<br>
<b>Sent:</b> Saturday, August 31, 2024 9:31 AM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:at@lists.antique-tractor.com">at@lists.antique-tractor.com</a><br>
<b>Subject:</b> Re: [AT] 3020 electrical, continued...
"resistance wire"?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p>The only experience I have with coil resistors was on older
Chrysler products that used a block type resistor usually
mounted near the coil. The purpose was not to protect the coil
but to protect the points. Running 12V through the points
would cause them to burn quicker than running only 6V.<span
style="mso-ligatures:none"><o:p></o:p></span></p>
<p>The resistor was wired in such a way that when starting there
was 12V to the coil as it was tapped off of the solenoid wire,
but when you put the key back to run, the coil was powered
through the ignition switch, through the resistor and was only
getting about 6V.<o:p></o:p></p>
<p>The resistors were potted in a ceramic block and mounted in
the open as they would generate heat from dissipating that
excess 6 volts. If the resistor failed the engine would start
but die as soon as you dropped the key back to run. It was
fairly common, easy to diagnose and easy to fix by replacing
the resistor. Like any light bulb, they just burned out at
random times.<o:p></o:p></p>
<p>It sounds like your 3020 is kind of wired that way. If you
are seeing no resistance on the wire, it may have been
replaced in the past or the resistor has been removed. It will
run, but will be hard on the points. If it was a resistance
wire it would have been left out of the harness to dissipate
the heat.<o:p></o:p></p>
<p>Hope this helps,<o:p></o:p></p>
<p>Stuart<o:p></o:p></p>
<div>
<p class="MsoNormal">On 8/31/24 00:11, Dean Vinson wrote:<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal">Tinkering with the 3020 yesterday and I
opened up the dashboard panel to see what was behind it, and
found a rosy colored mousenest decorated with the insulation
from a formerly-red wire stringing back through there.
There’s a three-inch section of wire where the copper
strands are exposed, oxidized dark but still intact with
good continuity. <o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I can replace the wire easily enough, but
I’m trying to get my head around its function. Near as I
can tell from the wiring diagram it’s a “resistance wire”.
It’s one of two wires connected to the input side of the
coil, the other one coming from the starter solenoid.
Service manual wiring diagram shows it coming from the
ignition switch, but this one comes from a circuit breaker
mounted below the ignition switch. It’s outside the
harness so presumably a replacement for an original wire
that failed at some point.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">The battery is a 12-volt and the parts
manual says the coil is a 6-volt. Resistance across the
coil tests at 2.8 ohms, and 12V applied at the input side
tests at 12V at the output side, both of which suggest this
coil is a 12-volt rather than 6 (according to some websites
I found with tips on how to tell the difference).<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">So if the “resistance wire” was intended
to protect the 6-volt ignition system from the 12-volt
battery, but the OEM coil was replaced with a 12-volt, do I
need to replace the wire or can I just remove it and call it
good?<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Dean Vinson<o:p></o:p></p>
<p class="MsoNormal">Saint Paris, Ohio<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><span style="mso-ligatures:none"><br>
<br>
<o:p></o:p></span></p>
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