Farmall 140 will not shut off

[JP Cole]

I have a 1978 Farmall 140 (12v system) that has started doing weird things! It started off with the tractor just shutting off Iile youd turn the switch offI changed plugs, points, condenser, coil, plugs and plug wires! Problem solved.now when I start the engine it will not turn off with the key! If I unplug the lower wire of the external resistor that is mounted to the alternator I can crank and shut the engine off from the switch! I changed the resistorit still does it! I tried to run the wiring schematics on it and thought maybe that the ammeter was bad since it runs through that! Replaced that and still will not shut off!!! Any help would be appreciated!!
JP

 

[Steve@Advance]

What size resistor is there at the alternator, and does one end of the resistor go to the #1 plug terminal on the alternator?

The resistor needs to be a 10 ohm, 10 watt resistor. If the ohm rating is too low it will feed back and make the engine continue to run.

 

[used red MN]

Can you tell us if the wiring is absolutely stock or have modifications been made? Are you sure you reconnected the wires to the coil as they were before you changed it? I do not have access to a stock wiring diagram for the later 140 with the internal regulated alternator. If the resistor Jim is talking about would have went bad or failed the normal result would be that the alternator would stop charging. It would be an unusual failure mode for it to short circuit and keep continuity between it leads or terminals. This is what would need to happen for it to not shut off. Any chance you could give us a picture of the wiring connections at both the coil and the resistor by alternator?

 

[Rich'sToys]

Often there is a diode in one of the wires which will keep it from running on after the switch is shut off. Is it possible that that might have failed?

 

[JP Cole]

Not sure where that diode is? Can you tell me where to look?

 

[JP Cole]

(quoted from post at 08:34:46 03/21/23) Can you tell us if the wiring is absolutely stock or have modifications been made? Are you sure you reconnected the wires to the coil as they were before you changed it? I do not have access to a stock wiring diagram for the later 140 with the internal regulated alternator. If the resistor Jim is talking about would have went bad or failed the normal result would be that the alternator would stop charging. It would be an unusual failure mode for it to short circuit and keep continuity between it leads or terminals. This is what would need to happen for it to not shut off. Any chance you could give us a picture of the wiring connections at both the coil and the resistor by alternator?

I will take pictures of both connections at the cool and resistor and post them to see if you can tell if it s not right! I feel pretty sure that I wired the coil back up just as it came off but is there a way to double check that? Or do I just switch them around and see if that fixes it?

 

[JD Dave]

All of the comments are helpful. The bottom line is that you're getting a feedback of 12 volts to the coil somehow which is bypassing the ignition switch. You should troubleshoot armed with the electrical schematic and a multimeter searching for a stray voltage in the circuits.

 

[JP Cole]

I think that was probably gonna be my next step! I just need a good schematic of this tractor! Im pretty sure that the wiring is NOT factory wiring I dont believe! So it may end up being a pain!

 

[JP Cole]

Pretty sure that its NOT stock wiring I dont believe! As far as the resistor, I ordered it through Amazon I think ! It said in the description that it is the replacement resistor for the original one used on the Farmall 140.BUT not sure I would exactly trust that or not? I will look at my order to make sure its the correct resistor and if not.I have the original one that was on it still! Ill put it back on and see if that makes a difference!

 

[crsutton81]

The first 2 photos are for the very last 140s made with the factory alternator and hazard flashers on the fenders.

The next 2 pic's above is for the next to last wiring schematic that was used. This setup utilized a factory 12v system with a generator and hazard flashers on the fenders. There were a total of 5 different wiring changes in the 140 production run to my knowledge. Hope this helps.

 

[NDIHC]

It started with he tractor engine just shutting off for no reason. So some ignition parts were replaced. Was there any troubleshooting done to determine where the fault may have been? Did you lose power to the ignition system components such as to the coil or through the coil to the points? Was the condenser bad, shorted out? Points not opening and closing to induce a spark? Or were parts just replaced? My first thought would be that the ignition switch should be tested to make sure it is open on the off position only and closed in the on position only. Easily tested with a test light to make sure that it actually turns on and off properly. Or with the switch disconnected, test with an ohm meter.

 

[JP Cole]

I actually talked to another friend of mine that worked with Farmall/McCormick for over 30 years and he told me to do a complete tune up when the tractor first just shut down! It was working fine prior to that! So Im guessing its probably a shorted wire or pinched a wire somewhere I just dont know where to start looking!!

 

[JP Cole]

Oh man.thanks for this! Tomorrow I will start troubleshooting for shorts or grounds! Thanks again!

 

[Janicholson]

This is the correct answer!!!! The alternator is feeding power through the #1 terminal back to the ignition resistor. It needs a 10 ohm 10 watt resistor (or a side marker light light bulb (not LED)) wired in series in that wire to #1 terminal. Jim

 

[crsutton81]

While checking, look closely at the power wire that runs from the key / kill switch to the +(pos) post on the coil. If it's still original, it's a very fine Guage of wire and I have had instances where it partially broke or rubbed on the engine head and caused weird stuff to happen. You could have dislodged it enough while replacing the coil for it to run, but still be shorted out partially and causing the alternator to overcome the system ??

 

[used red MN]

I realize he is trying his best to help you but the diagram Mr. Sutton posted is not a true wiring diagram. So in my opinion it is not really of much value for what you have going on. I would say that the wiring on your tractor does appear to be stock as from the factory. I would like to know if the tractor will run with one of those wires unplugged off the resistor? This will tell us if the resistor is associated with the alternator circuit or the ignition circuit. My second request may be a little more difficult. There is a plug with two wires plugging into the alternator on the engine side. It looks like there may not be enough room to unplug it without taking the alternator belt off and sliding the alternator all the way out in its adjustment slot. You may need to pinch the small tab on the front of the plug back against it to release the plug. I would also like to know if starting with that wire unplugged will allow it to shut off properly. Running with either of these unplugged for testing will not hurt the tractor.

 

[gene bender]

you dont have a short or it would not run nor a ground same it would not run. You are still getting voltage to the coil with key off so thats why it stays running

 

[Jim.ME]

The parts list shows the resistor for the alternator (item key 19). Your picture shows the upper wire going to the #1 (excite) terminal of the alternator. You posted it will run and shut off if the lower wire connection (two wires in it) is unplugged from the resistor. Without a true wiring diagram, I am guessing that connector was used as a junction with one of those two wires bring power from the ignition switch. That would excite the alternator through the resistor and the other wire goes from there to the coil to power the ignition. As has been suggested, I would suspect the resistor is bad or the wrong resistance. Try the old resistor you took off to see if the problem is still there.

Edit: Further looking on Amazon I see the resistors for use with a 6-volt coil when used in a 12-volt system; I don't see the higher resistance one needed to use in the excite circuit of an alternator. Can you post the info on the resistor you purchased?

This post was edited by Jim.ME on 03/22/2023 at 04:36 am.

 

[BarnyardEngineering]

(quoted from post at 15:59:47 03/21/23) Pretty sure that its NOT stock wiring I dont believe!

Pretty sure it IS stock wiring. The picture you show is of stock wiring. It's a 1978 model so it had a lot of modern features the older versions did not have. Alternator. Starter solenoid. Key start. Clutch safety switch.

Going forward, troubleshoot first. Don't just throw parts at it, because you're just as likely to be digging yourself a deeper hole than you are fixing it based on a guess. Case in point, the ammeter. It has NOTHING to do with your problem. The ammeter just reads Amps. It does not have any switching capabilities. It is no different than a piece of wire for passing electricity. If the tractor starts and runs and the needle moves, it is fine.

 

[Hobo,NC]

The resistor for the alt switch wire is CASE IH PART # 107558C1, 25 OHM RESISTOR.

The one you posted looks like a ICR13 1.82 ohms.

I have never use the 107558C1 but had a bud that's all he used for the switch wire on a 10SI. You need to ohm that resistor.