Ford 8N Ignition and Resistor

[jpsheb]

Hello all,

I have a question regarding my 1949 Ford 8N tractor. It has been converted to a 12V system (before I purchased it). It's haveing some trouble starting now--no spark, and as I look over the system, I notice that the coil says "External resistor required". However, the supply wire to the coil goes straight to the ignition switch--no resistor in the path. There is a resistor mounted forward of the distributor, but it's not connected to anything.

Will this be a problem? (The tractor has run fine most of the time for the year that I've had it, in spite of this).

Thanks!

-Jack

 

[whodat526]

Hello all,

I have a question regarding my 1949 Ford 8N tractor. It has been converted to a 12V system (before I purchased it). It's haveing some trouble starting now--no spark, and as I look over the system, I notice that the coil says "External resistor required". However, the supply wire to the coil goes straight to the ignition switch--no resistor in the path. There is a resistor mounted forward of the distributor, but it's not connected to anything.

Will this be a problem? (The tractor has run fine most of the time for the year that I've had it, in spite of this).

Thanks!

-Jack

yes it will cause the coil to burn out u either need a resitor or a coil with the internal resitor

 

[dennis54]

I have an 8N that is converted to 12v. I have a resistor before the 6v coil and have no problems. However, there are 12v coils available for the front mounted distributors of the early 8N's.

 

[whodat526]

u still need a resistor unless the coil has printed on it that it as a internal resistor

 

[jpsheb]

Thanks for the info. It looks like it has a resistor, mounted just forward of the distributor. But it is hooked to nothing! What configuration to I hook to the resistor to the coil in? (does it just go in series between the positive side of the coil and the starter switch?

I'd really like to post photos (worth a thousand words), but the posting feature only allows a URL. Is there a way to upload photos and attach them to posts like this?

Thanks again!

 

[whodat526]

yes the resistor goes between the switch and the coil

 

[jgayman]

I'd really like to post photos (worth a thousand words), but the posting feature only allows a URL. Is there a way to upload photos and attach them to posts like this?

Thanks again!

When you post your reply, choose the "insert image" icon and then scroll down the page to the "additional options" section and you will see the "manage attachments" button. Click the button and it will then allow you to insert photos directly. There is a size limit so you may need to scale-down the size of the image beforehand.

- John

 

[Soundguy]

just to be clear on a few things.

the front mount coils have a single terminal, and the side mounts have 2.

it is possible to gut a front mount coil, and run wires out of it and use a round coil.

you can get round coils for 12v that don't need a external resistor.. the napa IC14SB

the 12v marked front coils STILL need a resistor.. their impeadance is only 2.5 ohms, and was meant to be run in tandem with the oem ballast resistor back on the dash.

as for 'internal resistor' coil terminology.. that is archaic. you will be hard pressed to buy a modern made ignition coil today that atually includes a resistive element, vs just have the correct number of turns of primary and secondary wire, of the correct diameter to make up its primary and secondary impeadance.

running on 12v with to low a value coil leads to reduced breaker life and coil life, and thus weak or no sparks, and thus, bad running and hard starting as the points surface area arcs, pits and erodes faster than designed, and the coil primary insulation potting melts and allows thermal damage between windings and then you start getting shorted turns. as more turns short, current goes up and resistance goes down heat goes up.. it causes a cascade effect... round coils.. at least modern ones are oil filled and disipate heat much more efficiently than the older front mount, square oem tar potted ones, or the newer epoxy potted ones.

soundguy

 

[jpsheb]

Ok, in my greenhorn ignorance, I thought my tractor was an 8n. It was actually a 641! (I did not grow up with tractors and don't know many people with them, so I'm having to teach myself).

Update: I replaced the coil with aone with an internal resistor. I also replaced the plugs (w/ hotter ones), point, and caps. Now, it starts with no problem. Still diesels, but that's a different problem!

 

[Soundguy]

is it dieseling.. or is it running on due to no ignition isolation?

soundguy

 

[jpsheb]

That I'm not sure...I just know that when I turn off the ignition switch and remove the key it sometimes continues to run. Is that something I can check with my timing light? (i.e., will the ignition system continue to spark in the case of no ignition isolation?)

-Jack

 

[Soundguy]

easier than that.. just pull the primary wire going to the coil. if that kills it, you are still getting power to the coil with key off. most lielly cause of that when you have a 3 wire alt is no isolation in the #1 excitation line.. or incorrect isolation. less likely it's a bad key switch.

post back

soundguy