[AT] One of those days
Stuart Harner
stuart at harnerfarm.net
Sat Jan 24 12:26:59 PST 2026
Dean,
A couple of things come to mind.
The switch may be leaking internally and an oil film my be messing with
the connectivity of the switch. Adding resistance where there should be
none.
Some piece of debris has entered the switch diaphragm and is causing
erratic behavior.
In either case, switch replacement may be the only answer.
One other thing to check is continuity between the base of the switch
and the negative battery post. A corroded or otherwise compromised
connection somewhere in the circuit could be showing up as fluctuating
voltage.
If possible put a voltmeter or amp meter between the battery post and
the negative cable and monitor the circuit at that location. If that is
steady while running. I think the switch is your culprit.
Best of luck,
Stay warm and dry if possible.
On 1/24/26 13:30, Dean Vinson wrote:
>
> Thank you, gentlemen. It certainly seems logical that the issue is
> more likely to be the sensor or the wiring rather than an actual
> pressure failure. I’m still not seeing an obvious explanation for
> what would make the problem suddenly pop up in between when the guys
> at the repair shop had the tractor running and when they dropped it
> off, but I guess that’s less important than fixing it.
>
> I talked with the shop again and they plan to send a technician here
> to my place to check it out. Might be a while before they get me back
> on the schedule but I told them I won’t need to use it for anything
> during the winter anyway.
>
> In the meantime I did tinker with it a little more, trying to test the
> sender by disconnecting the idiot light wire and then using a
> multimeter to check for voltage between the tip of the sensor and the
> positive terminal on the battery. With the engine off I got 12.57
> volts, which made sense: No pressure, switch closed,
> positive-to-ground circuit complete. With the engine running I
> couldn’t get any kind of consistent reading—the meter reading just
> fluctuated wildly all over the place no matter how carefully and
> steadily I held the test prongs. I’m not certain how to interpret
> that, but I guess if the switch were simply open there’d be current
> flow and no voltage at all (i.e., idiot light “off”) so I’m taking it
> as an indication of a sensor failure.
>
> It’s kind of hard to get a good look at the sending unit, much less
> get a hand on it, because it’s slightly behind the power steering
> pump. Wrenching on an oily hunk of metal to get that pump out of my
> way, in 10°F weather, is not terribly high on my list of fun things to
> do so for now at least my plan is to let it sit and wait for the
> repair shop guy to get here.
>
> Lots of snow coming shortly, by all accounts, so that’ll keep me
> occupied for a while anyway. Spencer, I’m guessing you might be in the
> ice/freezing rain path? One of my brothers lives north of Atlanta
> and is tracking that risk.
>
> Dean Vinson
>
> Saint Paris, Ohio
>
> *From:*AT <at-bounces at lists.antique-tractor.com> *On Behalf Of
> *Spencer Yost
> *Sent:* Friday, January 23, 2026 8:59 AM
> *To:* at at lists.antique-tractor.com
> *Subject:* Re: [AT] One of those days
>
> I’ve had a few oil pressure sending units fail. Granted, they
> typically were full failures and didn’t work at idle either, but I
> could see how the failure mode might be vibration induced.
>
> I’d get a super cheapie oil pressure gauge at the auto parts store, or
> this:
>
> Engine Oil Pressure Test Kit
> <https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html?hftm_sc=&hftm_source=google&utm_source=google&utm_medium=cpc&utm_campaign=21901271210&campaignid=21901271210&utm_content=171677806502&adsetid=171677806502&product=62621&gad_source=1&gad_campaignid=21901271210&gbraid=0AAAAADAHb4eil-ADMAET3vLnfQyDpklM->
>
> harborfreight.com
> <https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html?hftm_sc=&hftm_source=google&utm_source=google&utm_medium=cpc&utm_campaign=21901271210&campaignid=21901271210&utm_content=171677806502&adsetid=171677806502&product=62621&gad_source=1&gad_campaignid=21901271210&gbraid=0AAAAADAHb4eil-ADMAET3vLnfQyDpklM->
>
> remove the sensor, and then hook it up to confirm if you have a real
> problem.
>
> Spencer Yost
>
>
>
> On Jan 22, 2026, at 10:44 PM, Dean VP <deanvp at att.net> wrote:
>
>
>
> Dean,
>
> My guess would be a faulty sensor or a loose wire shorting out
> somewhere due to the vibration of the running engine. I sincerely
> doubt you have an oil pressure issue. Check everything around
> areas where your shop may have worked. I think they damaged or
> disturbed something while working on the other stuff. Is there
> any wiring that they could have disturbed?
>
> Dean VP
>
> On Thursday, January 22, 2026 at 08:19:55 PM MST, Dean Vinson
> <dean at vinsonfarm.net> wrote:
>
> Dean, ah, I see now how my sale of the 620 is coming back to haunt
> me. :)
>
> On the plus side for green tractors, my 3020 runs like a top and
> is standing by in the barn with the rear blade attached, ready for
> the snowplow duty that per the weather forecast looks mighty
> likely in the coming few days. Moving 8 or 10 inches of snow with
> a rear blade is not ideal but it beats relying on my scoop shovel.
>
> (Speaking of not ideal, the high temperature for the day after the
> snowstorm is currently forecasted to be 7°F and of course the 3020
> is an open-station tractor. “Cab by Carhartt,” as the saying goes.)
>
> The oil pressure warning light issue on the Ford 3600 does concern
> me a little. The idiot light comes on when the key is turned on
> but prior to starting the engine, exactly as it should to
> demonstrate that the circuit is intact and the bulb works, then
> goes off once the tractor starts and oil pressure builds enough to
> open the pressure sensor switch. The only surprising part is
> that the light comes back **on** when I throttle up. One
> possibility is that there is a glitch causing a “false positive”
> warning light even though oil pressure is fine. The other is
> that the sensor and wiring are functioning exactly as intended and
> oil pressure is for some reason dropping.
>
> Today I added about a third of a quart of oil to bring it up to
> the “Full” line on the dipstick, and I removed, inspected,
> reconnected, and fiddled with the idiot light wire where it clips
> onto the oil pressure sensor just to make sure it felt secure.
> Neither of those actions stopped the warning light from coming on
> as soon as I throttle up past idle, but it seemed worthwhile to
> try them just in case.
>
> The repair shop hasn’t called me back yet, so I’ll follow up with
> them tomorrow. The timing of this issue—literally popping up in
> the first few seconds after they brought the tractor back to me
> after working on it—makes me wonder if something they did somehow
> caused this, maybe by aggravating an existing problem enough to
> push it from “this is going to fail soon” to “this has failed.”
> But maybe it’s just a coincidence. Either way, I can’t use the
> tractor with the oil pressure warning light on.
>
> Dean Vinson
>
> Saint Paris, Ohio
>
> *From:*AT <at-bounces at lists.antique-tractor.com> *On Behalf Of
> *Dean VP
> *Sent:* Thursday, January 22, 2026 2:36 AM
> *To:* Antique Tractor Email Discussion Group
> <at at lists.antique-tractor.com>
> *Subject:* Re: [AT] One of those days
>
> Dean,
>
> I've had all too many days like that. it can be exasperating. As I
> get older, they seem to come more often. Lost items can usually be
> better described as misplaced items. Absent minded excellence.
> I'm really good at that. But in your case, it is all because you
> sold the JD 620. If you had sold the M you would only have had 5
> nuts to contend with rather than three, but the advantage is
> missing one out of 5 is not nearly as serious as one out of
> three. But eventually you will see the light! :-)
>
> But I will admit I have never had the light sequence you are
> experiencing. Probably because JD did not use idiot lights on the
> two-cylinder tractors. But it is exactly opposite of what one
> might expect. Is it possible that with your multiple tractors you
> have forgotten how this one is supposed to work? I don't recall
> any piece of machinery that that has worked like that except my JD
> 750 Compact Tractor. It has a light on the dash that turns on
> when the key is turned on and stays that way and is not dependent
> on RPMs. Since I too have multiple tractors and this is the only
> tractor that works this way, it has more than once caused me to
> stop and question what is wrong. Then I realize this is the way
> this one works.
>
> I cannot think of an oil pressure sensor could possibly fail
> backwards. This will be interesting when you find out what is
> going on.
>
> The other Dean in AZ
>
> Dean VP
>
> On Wednesday, January 21, 2026 at 04:53:43 PM MST, Dean Vinson
> <dean at vinsonfarm.net> wrote:
>
> Minor tinkering today with my Farmall Super M, chainsaws, and Ford
> 3600. Nothing quite went as expected.
>
> This morning I went into town to pick up the Super M’s right front
> wheel, which a local tire shop had finished pulling thorns out of
> and putting a new tube into. When I got home I went to put it
> back on the tractor, which is sitting by itself on the
> (relatively) clean concrete floor in the far corner of my enclosed
> shop. Got the rim in place and went to bolt it back on, only to
> discover I was short by one nut. Neat little pile of hardware on
> the floor right where I’d left it, three bolts, three lock
> washers, but for some reason only two nuts. Couple of wrenches
> nearby but nothing else, no junk, no random stacks of supplies or
> half-full jugs of engine oil, nothing to camouflage the presence
> of the missing nut. (My shop is not exactly short of any of
> those things, but they’re all over on the other side near the
> workbench where I spent most of my time, not here where the
> tractor’s been sitting.) I got down low and looked, picked up
> the wrenches and put them back down, checked under the other front
> wheel, checked the area, nothing. Big dang nut for a 5/8” bolt
> just disappeared. Scratched my head for a minute but soon enough
> gave up and went back into town to visit the local hardware store
> for another nut. Problem solved, tractor is now all back together.
>
> Next task was to clean up my two chainsaws and figure out why one
> of them wouldn’t start last time I tried to use it. I take both
> with me when I’m clearing osage orange and honeysuckle from the
> old overgrown pasture. The newer saw cuts clean wood, and the
> older saw with a no-longer-fresh-but-still-halfway-okay chain cuts
> stumps down low and serves as the backup in case I get the other
> one pinched. Last time I went out I absolutely could not get the
> #2 saw to start, but it’s been an egregiously long time since I
> cleaned (much less replaced) the air filter. So today I got the
> saw all cleaned up, and also cleaned up the other one while I was
> at it, but didn’t see anything that looked bad enough to keep the
> saw from running. Scratched my head for a while and then finally
> thought to check the fuel tank, which of course turned out to be
> bone dry. Last time I went out I must have somehow forgotten to
> fuel that one up. This was mildly funny to me today, but it had
> not seemed so last week when I was out there in the woods yanking
> endlessly on that starter rope and scaring away wildlife with a
> loud string of curses.
>
> Last task was to take delivery of my Ford 3600, which for several
> weeks had been at a local shop for an overheating problem. The
> shop’s diagnosis, as written on the completed service order, was
> that the “coolant was nasty and radiator was almost plugged.”
> They removed the radiator, sent it out to get cleaned, then put it
> all back together, function checked it, and brought it back to me
> late this afternoon. After their driver started it up and idled
> it backwards down off his tilt-bed truck, I went to put it in the
> barn…and as soon as I throttled it up past idle, the oil pressure
> light came on. I tried throttling down again and then back up,
> and shutting the tractor off then restarting, but same thing every
> time: Charging system and oil pressure lights come on when key is
> turned to the “run” position, then both go off when the tractor
> starts, but the oil pressure light comes back on at anything above
> a moderate idle and goes back off upon returning to idle speed.
> I checked the oil level and it’s about halfway between “Full” and
> “Add” on the dipstick, so I wouldn’t expect it to just be an oil
> level issue. Their driver hadn’t left yet so he called his
> service manager and gave him the rundown, but by then it was
> nearly five o’clock so the plan is they’ll call me in the morning
> and figure out the next step. I won’t need the tractor for
> anything until springtime, but still, dagnabbit it I was looking
> forward to having them all back home and in one piece today. :)
>
> Oh, and of course, as I walked back through the shop to close up
> the doors and turn the lights off, I stumbled across that missing
> nut about 15 or 20 feet from where the Super M is parked. Maybe I
> somehow kicked it over there without realizing I’d done so, or
> maybe a cat had been entertaining itself, who knows. But now I
> have an extra 5/8” 11-pitch nut in a shop drawer, in case I ever
> need one.
>
> Dean Vinson
>
> Saint Paris, Ohio
>
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