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

[John Hall]

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 
> <mailto: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
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.antique-tractor.com/pipermail/at-antique-tractor.com/attachments/20210827/6da7b4e4/attachment.htm>