3 cylinder thousand series ignition circuit question

Sean in PA · Jan 22, 2018

Over on another tractor board someone just pointed out a drawing in the Ford factory service manual for the 1965-1974 thousand series tractors. In the Electrical section, on page 46, it is figure 56. It shows two different setups for the wiring to the coil primary from the key switch. One setup has the resistance wire and the starter bypass wire and it says those are for the 5" coil, and the other setup shows a non-resistance wire and no bypass, and it says that one is for a 5-1/2" coil.

Does anyone know which tractors got the 5-1/2" coil that didn't use the resistance wire? was it on certain models, or after a certain date on all models? I can only find reference to a single part number for the coil on the parts site, and it looks like it's for the one that uses the resistance wire.

Has anyone ever seen one that came from the factory with the 5-1/2" coil and no resistance wire?

da.bees · Jan 22, 2018

The coil has probably been replaced more than once so rather than going at it like that,pull your coil to see if it say's "use resistor",internal resistor" or something similar that let's you know wherether coil has internal resistor or require's external resistor.. When you see which coil is on your tractor,here's how you tell wherther the wire is (A)non resistor,no bypass (B)resistor with bypass. Test battery voltage between posts. To protect your meter from damage,pull secoundary coil wire from coil and dis-connect primary from dist side of coil. Turn key to run but don't start tractor then emediatly test voltage at Bat screw on coil. leave key on for 2 minutes then test again. If either or both tests show same as volts between battery posts,you have non-resistor wire/no bypass and that conclude's test. If either show less than battery volts,you have resistor wire. To see if you also have bypss while starting,test volts at coil primary Bat screw while turning engine over with starter. If volts are same as between battery posts,you have bypass in addition to resistor wire.

Destroked 450 · Jan 22, 2018

Found it in my manual as well, parts search only shows one coil, looking through my 1982 factory parts book only shows one coil.

Considering the older 6 volt tractors didn't use a resistor wire I'm wondering if some of the very early -000 series where built without the resistor wire and a change was made later during the production run.
My service manual list the resistance values of both coils but gives no reference as to when or why the change was made.
Nothing in my parts book refers to a different wiring harness, key switch or any other part being different.

My guess is any one who replaced the older wiring harness would have gotten a replacement harness with the resistor wire.
Probably drove a few guys nuts trying to figure out why their tractor would not run properly after they had installed the new wiring harness.

Sean in PA · Jan 22, 2018

(quoted from post at 12:23:33 01/22/18) The coil has probably been replaced more than once so rather than going at it like that,pull your coil to see if it say's "use resistor",internal resistor" or something similar that let's you know wherether coil has internal resistor or require's external resistor.. When you see which coil is on your tractor,here's how you tell wherther the wire is (A)non resistor,no bypass (B)resistor with bypass. Test battery voltage between posts. To protect your meter from damage,pull secoundary coil wire from coil and dis-connect primary from dist side of coil. Turn key to run but don't start tractor then emediatly test voltage at Bat screw on coil. leave key on for 2 minutes then test again. If either or both tests show same as volts between battery posts,you have non-resistor wire/no bypass and that conclude's test. If either show less than battery volts,you have resistor wire. To see if you also have bypss while starting,test volts at coil primary Bat screw while turning engine over with starter. If volts are same as between battery posts,you have bypass in addition to resistor wire.

Thanks. I know how to diagnose which type of coil I have.

I was asking about the two different kinds of coils referenced in the service manual simply as a quest for knowledge.

As far as I knew up to the point that I looked at that diagram in the service manual, the '65-'75 thousand series gassers had all come from the factory with the resistance wire and starter bypass, so I was just asking if anyone here had actual knowledge of any that had come form the factory with the coil that did not require the resistance wire.

Sean in PA · Jan 22, 2018

Considering the older 6 volt tractors didn't use a resistor wire I'm wondering if some of the very early -000 series where built without the resistor wire and a change was made later during the production run.

Destroked - Thanks. After thinking about your response, I thought that it makes sense that they might have started the production run using a true 12 volt coil and no external resistor and then switched to the lower ohm coil with the external resistance wire and the starter bypass to make them easier to start. Must have been very early on when they switched as I have never heard of anyone having one that came that way... but by now anyone that buys one that's setup with a true 12 volt coil and no bypass would assume that it was replaced at some point after it was new.

rvirgil_KS · Jan 22, 2018

?dis-connect primary from dist side of coil.......... test voltage at Bat screw on coil?

With the wire from coil to side of distributor disconnected, you have no ground return through the points so, with switch on you have no current flow and should see battery voltage at input of the coil regardless of amount of resistance that may or may not be in the wire.

To check for resistance wire, ground one end of the wire going from coil to side of distributor (this simulates closed points completing the primary coil circuit.) Turn on switch and measure voltage at input to the coil with switch on. If you have near battery voltage = no resistor. If you have approximately half of battery voltage = resistor or resistance wire.

?To protect your meter from damage,pull secoundary coil wire from coil ...? Not necessary, you are not measuring coil output pulse.

Sean in PA · Jan 22, 2018

(quoted from post at 20:27:42 01/22/18) ?dis-connect primary from dist side of coil.......... test voltage at Bat screw on coil?

With the wire from coil to side of distributor disconnected, you have no ground return through the points so, with switch on you have no current flow and should see battery voltage at input of the coil regardless of amount of resistance that may or may not be in the wire.

To check for resistance wire, ground one end of the wire going from coil to side of distributor (this simulates closed points completing the primary coil circuit.) Turn on switch and measure voltage at input to the coil with switch on. If you have near battery voltage = no resistor. If you have approximately half of battery voltage = resistor or resistance wire.

?To protect your meter from damage,pull secoundary coil wire from coil ...? Not necessary, you are not measuring coil output pulse.

Thanks, but again, like da.bees, you missed my point. I know how to check what type of coil I have and whether it needs an external resistance.

I am trying to educate myself (and hopefully others here) about how they came from the factory. I am trying to find out whether any 1965-1975 thousand series tractors actually came from the factory with a coil that did not require an external resistance.

3 cylinder thousand series ignition circuit question

Sean in PA

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da.bees

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Destroked 450

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Sean in PA

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Sean in PA

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rvirgil_KS

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Sean in PA

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