Farmall M electrical........

Bill in IL · Aug 1, 2008

My old M has me scratching my head. Tractor normally starts and runs good, generator charges marginal (think I need to tighten the belt) but it keeps the battery up. When I go to use the lights on high ampmeter shows discharge then eventually tractor dies just like it was shut off not immediatly but a minute or two later. Try to start it and it will crank but not fire. Let the tractor sit for half an hour and it will fire right up like nothing happened.

Bob · Aug 1, 2008

Check the battery voltage and the voltage at the ignition switch before and after turning on the lights. The battery should be near 7.4 Volts, if the charging system is doing it's work. (ASSUMING it's still a "6-Volt" system.) The voltage at the ignition switch, and leaving the ignition switch should track the battery voltage, with very little voltage drop. (Which could be caused by a dirty or corroded connection or a failing ignition switch.)

On top of a weak battery, the ignition system may be very marginal, due to a weak coil or other defect, and the drop in system voltage may be enough to make the spark too weak to fire the plugs under compression. Some weak coils will "recover" after cooling down.

Janicholson · Aug 1, 2008

I agree with Bob,
Ill also ask you to tighten the belt to make it spin for sure.
If it is regulator equipped, it should hold the lights with no discharge above 1/2 throttle.
if it does not use John T charging systm steps to make it right. JimN

John T · Aug 1, 2008

On the hot ignition problem, Id suspect a coil or possibly a condensor, if hot wiring to by pass the ignition switch makes her run, suspect bad switch contacts. In the meantime tighten the belt and insure good grounds and wiring connections on the charging system. Heres the link to charging troubleshooting if needed..

John T
Charging Troubleshooting

Red Mist · Aug 1, 2008

(quoted from post at 12:21:59 08/01/08) My old M has me scratching my head. Tractor normally starts and runs good, generator charges marginal (think I need to tighten the belt) but it keeps the battery up. When I go to use the lights on high ampmeter shows discharge then eventually tractor dies just like it was shut off not immediatly but a minute or two later. Try to start it and it will crank but not fire. Let the tractor sit for half an hour and it will fire right up like nothing happened.

Bill - what about when you don't use the lights - does it run all day long? Hard to believe the lights would kill the battery in two minutes. Sounds more like a bad coil or condenser. When condensers go bad, they often go bad for good, whereas coils go bad intermittently, especially when they get hot. After they cool off, they often come back. mike

Bill in IL · Aug 1, 2008

I recently replaced the condensor and points so I don"t suspect that. Coil maybe but the only times it has died was when I turned on the lights one time as I was on the road in the dark.... bad news. Coils are cheap so I will swap it out. But I really don"t understand what the lights and their drain on the system is doing. Starter would whirl the engine over very well after it died just would not fire. I guess like you guys said check all the grounds thats always good advice on electrical stuff.

How do you tighten the belt? I know you loosen the setscrew and suppose to change the pitch on the pulley by turning half of it but how do you turn it and fight the belt? Suggestions would be appreciated.

Bill in IL · Aug 1, 2008

Yes it will run all day long without using the lights.

Brownie 450 · Aug 2, 2008

Check for a terminal lug in the ignition primary wiring which might be down to 1 or 2 strands of wire making contact. Pull firmly on suspected connections to locate problem areas.
I believe that the coil is running on low voltage due to a high resistance, & turning the lights on drops the voltage enough more to lose spark.

Brownie 450 · Aug 2, 2008

Got to thinking---we had this trouble on the MTA, & it was the ignition wire itself that was down to 2 strands inside of the harness where it goes over the valve cover. Actually caused trouble at the point where the harness was held with a clip at the front valve cover stud.
Bob's idea on voltage checks will show this up.

Farmall M electrical........

Bill in IL

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Bob

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Janicholson

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John T

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Red Mist

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Bill in IL

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Bill in IL

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Brownie 450

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Brownie 450

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