1974 FORD 4000 3 cyl ignition coil clarification

[TractorXav]

I have a question I have not been able to find the exact answer to and I hope one of you may be able to confirm for me. Even the Service manual is not clear on this.

I understand there are 6V coils and 12V coils and that some tractors came with a resistance wire and some don't. I assume the resistance wire came into play when 12V system started being used but 6V coils were still installed, but I can't tell for sure. Maybe the 6V systems also had a resistance wire...

So, in short, my tractor is running on 12V. Do I need for sure a resistor, either through a resistance wire or internal to the 12V coil? If the resistor is not because of the 12V system, how can I verify if I need it or not? I do not want to trust what the previous owner did (don't have a resistance wire installed right now).

Thank you.

 

[ovrszd]

Welcome to TBN.

My understanding is that the points need to run on 6V? So if you are using a 12V system/coil it needs to have an internal resistor to protect the points? Some older tractors had an external resistor. But I cannot verify if yours does.

Hopefully one of the Ford guys will chime in here with details. There are several very knowledgeable Ford guys here on TBN.

 

[Roadworthy]

You are correct in that some twelve volt vehicles did use a six volt coil. Some were even wired such that the ballast resistor was bypassed during starting for a hotter spark. To determine whether your particular application requires a ballast resistor you need to look at the electrical diagrams. Of course you'd be assuming the original coil was still in place - no guarantee on that being the case.

 

[RickB]

A 6 volt (unresisted) coil is correct for your 12v 3 cylinder 4000. There is a resistance wire built into the OEM wire harness between the ignition switch and coil. Every US built Ford gas tractor built from the time the 8N side mount distributor was introduced plus every Ford gas tractor built in the US, England or Belgium 1965 and later use the same coil, commonly described as a 6 volt coil.

 

[ovrszd]

Good stuff Rick!!! Thanks for chiming in!!!

 

[TractorXav]

Thank you guys.

I guess I need to check the wiring again (Tractor is unfortunately 1h away ...).

I only have one wire going to the coil. Looking at the manual, there are two set ups. One with a 5" coil, labelled "resistance wire", one with a 5.5" coil, labelled "non-resistance wire. Looking at the diagram in the manual, the "5 inch coil" (the one labelled "resistance wire") has 2 wires going to it, one from the starter relay, one from the ignition switch. The "5-1/2 in coil" (the one labelled "non-resistance wire"), only shows one wire ... So I thought I had the "non-resistance wire" which I understood was without a resistor in the wiring and therefore needing an internally resisted coil... Maybe it means something different, not sure. Long day, my brain is fried

 

[RickB]

What kind of manual do you have? You should have the non resisted coil and two wires connected to the + side of the coil. Could be your start solenoid was replaced at some time with the incorrect style and the bypass start wire was eliminated.
The small I terminal on the solenoid should supply full battery voltage to the coil when the starter is engaged.

 

[TractorXav]

I have the 1965-1975 Ford Tractor Service Manual.

I must add that the Tractor starts and run great, but after about 5-10min of running, it acts as it is missing fuel and will only run a low idle with full choke. After reading a bunch of posts and now with a revamped carburator, I was thinking the coil may be bad.

Would the tractor be able to start/run if that second wire was actually missing?

 

[RickB]

The second wire (from the start solenoid to the coil +terminal) supplies full battery voltage when cranking to facilitate starting. It is not energized when the starter is idle and many tractors start well without it.

 

[TractorXav]

Thank you Rick.

My next step is to check if I have that resistor installed or not when I get a chance to drive to the property. I'll post back with the results...