[AT] tractor electrical question--I think its fixed!!!

[Carl Szabelski]

Glad to here it’s resolved. Now I’ve got to find something else to work on.
Maybe something on that two year old list my wife has, or maybe not. Too
hot and muggy here in Michigan to do anything anyway. 90+ degrees with
about 80%+ humidity. No relief until middle of next week, unless Ida pushes
more warm and humid air North by then.

Carl

On Friday, August 27, 2021, John Hall <jtchall at nc.rr.com> wrote:

> I THINK the problem is solved!!!
>
> First let me say thank you to all who offered ideas--all ideas are
> appreciated when you have no idea where to turn next. If I try to reply to
> everyone, gonna be a cluttered mess of emails. If I don't mention someone
> who tossed out ideas or info, don't be offended.
>
> Special thanks to Carl for being so diligent researching this. It was nice
> to bounce ideas off someone doing the same research!
>
> Long story short, this system uses a resistor wire. Given time, it would
> get hot and fail. It is also noteworthy this is the HOTTEST tractor IH ever
> built by design (routing of exhaust mainly) so that pushes the heat even
> higher. So between this list, the Facebook IH Group, local starter shop, an
> older car mechanic, internet old car forums/groups, a custom car wiring
> harness builder and help from Ken Updike, I determined this system uses a
> resistor wire, not a coil with built in resistor. Internet searches on
> ignition systems give better explanation than me but I'll sum up how it
> works. Resistor wire feeds aprox 6V to coil, but during cranking the
> solenoid on the starter also actuates a bypass circuit to feed 12v for as
> long as starter is engaged (hotter spark, starts easier, especially in cold
> weather). The jumper wire proved something was going on once the system was
> hot. In researching I found that resistor wires are part of the harness,
> fail more often than you think, and the workaround is either buy a new
> harness or put on one of those ceramic ignition resistors with a separate
> feed from the key switch. These resistors were quite common on a lot of
> older cars, I picked one up at Oreileys. A lot of the old car crowd has
> posted doing this same thing. This setup still allows for the boost in
> voltage during cranking, where replacing the coil with a 12 internal
> resistor on its own wire would eliminate that feature.Note that all the
> original wiring must be left intact and hooked up!! I found no one selling
> resistor wire in quantities need for a repair such as this--probably part
> of the reason is who would really know the specs on the wire to know what
> to get. I did see mention of folks using a donor harness to salvage that
> wire.
>
> One thing that confuses a lot of people (including me until 3-4 days
> ago)--the voltage at the coil input WILL vary depending on if the points
> are open or closed--Greg Easley pointed this out if anyone wants to study
> further.
>
> Anyway, I ran the tractor for over an hour tonight mowing--I've ran out of
> big stuff to cut so pushing hard trying to get the temp way up was
> difficult, so I grabbed another gear and pushed pretty hard and got it as
> warm as I could. Also I had all the sheet metal off so it was probably
> running cooler as well. I'm pretty darn confident its now fixed, enough
> that I'm gonna get the haybine hooked up and cut some hay soon (I hope).
>
> One of the late comers to comment on this was Ken in AZ. I must say he
> nailed everything from what the wire is made of to how to work around the
> problem.
>
> Spencer, thanks for keeping this list going, the gang really stepped up on
> this one!!
>
> John Hall
>
>
>
>
>
>
>
> On 8/27/2021 4:52 PM, Carl Szabelski 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
>>
>>
>>
>
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