Farmall 140 1976-1977

[fitzchavis]

I have a farmall tractor with a serial number that falls between 1976 & 1977. What necessitates the requirement to install an inline ceramic resister at the coil? Currently, it does not have one? If anyone can give me direction I will appreciate it. Thanks.

[Gary Dotson]

As originally equipped from the factory, your tractor would have had an internally resisted coil, no resister would have been installed. You will only need a resister if someone has installed either a 12 external resister coil or a 6 volt coil. Replacement coils are generally marked with that info. If, for some reason, you are concerned about this, you can always disconnect the wire and check it with an ohm meter, the proper coil will be in the neighborhood of 3 ohms.

[fitzchavis]

As originally equipped from the factory, your tractor would have had an internally resisted coil, no resister would have been installed. You will only need a resister if someone has installed either a 12 external resister coil or a 6 volt coil. Replacement coils are generally marked with that info. If, for some reason, you are concerned about this, you can always disconnect the wire and check it with an ohm meter, the proper coil will be in the neighborhood of 3 ohms.

What reading should I get if there's no internal resistor inside the coil?

[Dave F.]

Most likely 1 ohm to 1.5 ohms from what I learned about coils. The 12volt coils that require a resistor should measure 1-1.5 ohms And the internal resisted 12v coils measure 3-ohms and 6volt coils measure 1-1.5 ohms so I would think you could use a non internal resisted 12 volt coil on a 6 volt. system providing the coil measures 1-1.5 ohms Dave F.

[Gary Dotson]

That’s correct, Dave. A 12 volt external resister coil is merely a 6 volt coil in disguise. I usually see 1.3 - 1.5 ohms on them.