Coil-12v or 6v

Recently acquired tractor. Previous owner converted to alternator. Once I replaced the solenoid, so itwould crank. No spark. Shine up points, no spark, test for power to coil good. test light on distributor side of coil, no blinky blinky while cranking. remove wires from coil test resistance with multi-meter, 0 resistance from input terminal to output terminal. Not shorted, but no resistance. Coil is bad-correct? So coil has been painted over, I can see no marking as to 6v or 12v. Wire to input terminal comes from a resistor. Is my coil 6v or 12v? And what do I replace it with? Thanks. gobble

You say converted to alternator, so it should be 12 volt negative ground now. You say the coil receives power through a resistor so it may well be a 6 volt coil. I would remove the old coil and resistor. Get a new 12 volt coil that doesn't require a separate resistor. Make sure the new coil is wired correctly when you hook it up (+= power, -= distributor if you have negative ground).

If you are checking across the + and - terminals, and getting an open reading, the coil is bad.

Getting the right coil can be a challenge without a vehicle to look up. And you can't always go by the part number on the box because being a near obsolete part, it may have been reboxed several times. Best take your ohm meter and check the resistance across the + and - terminals. For a 12v coil that does not need a resistor, it will have around 3 ohms resistance. A 6v will have around 1.5 ohms.

The NAPA number for a 12v coil that does not need a resistor is IC14SB. I don't know what it fits, but be a good idea to check it in the store just to be sure.

Tomturkey,I agree with what Jim.ME said 100%. A good 12 volt coil, no resistor needed is a NAPA IC14SB.

If you have a 12 volt system and the coil wire runs threw a resistor one has to reason you have a 6 volt coil.
That 6 volt coil with a resistor is used so you can bypass the resistor and supply a full 12 volts to the coil during cranking.
This gives you a real hot spark. Catch is you need the correct starter solenoid for it to work.

I would remove the old coil and resistor.
Get a true 12 volt coil and wire it direct from the key switch to the coil + side.
Napa IC14 is a good 12 volt coil.
If you want to save a few dollars you can get Napa IC14SB.

thanks, I thought as much but a bit unsure. gobble

Thank you Steve, I figured it was a 6v coil due to the resistor, but electricity is a very weak subject for me,needed some reassurance. gobble

thank you all help appreciated. gobble

Thank you John for you explanation and suggestion. I am always concerned about "letting the smoke out" on the electrical stuff. This may sound absurd, but I'd rather breakdown a tractor tire than work on electrical stuff. I converted two Farmall H's last winter to alternators. I just followed Bobs wireing diagram from the archives of this site worked out ok, but I am not very comfortable working electrical stuff. thanks again ?.gobble

(quoted from post at 18:20:14 11/20/18) Recently acquired tractor. Previous owner converted to alternator. Once I replaced the solenoid, so itwould crank. No spark. Shine up points, no spark, test for power to coil good. test light on distributor side of coil, no blinky blinky while cranking. remove wires from coil test resistance with multi-meter, 0 resistance from input terminal to output terminal. Not shorted, but no resistance. Coil is bad-correct? So coil has been painted over, I can see no marking as to 6v or 12v. Wire to input terminal comes from a resistor. Is my coil 6v or 12v? And what do I replace it with? Thanks. gobble

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"Not shorted, but no resistance."

To be correct, NO resistance = shorted, if yours is "open", it has the opposite of "no resistance", or "infinite resistance".

TomTurkey;
Thank you for posting this. I have had the same question, I just did not know enough about what was going on to even know what to ask. Thank you ALL for the input. When I get to that project, 1958 JD 420, I should be a lot further along now. Dsmythe

Bob, I really appreciate your posts on the yt forum. So much knowledge you freely share with others. When I read the trouble shooting procedure, the terms "open" "shorted" puzzle me. School me a little. If I check a 3 wire extension cord (hot neutral ground) and I have "continuity" on each wire from end to end is that also "open" but not shorted. But open in relationship to the coil is shorted. Electrical stuff is perplexing to me. I try to avoid it when possible. thanks for your comment. gobble

Will it run if you put the positive to the distributor? thanks

Yes it should run. Short version of why is; studies show it is harder for the spark to jump "backwards" at the plugs, accelerates plug wear and can cause misfires. Google "affects of auto ignition coil connected backwards" for more detailed info.

With all the scrambled eggs of diagnostic gibberish I assume you will change the coil with 12v without external resistor.
but what in all the threads indicates the distributor is making breaking the field?
testing a dist with a VOM is pretty much pointless( ha pun) with the condenser in place. A poorly installed set of points, or grounded connections, or short to case where it comes out from points/cond to coil, (or open) all can make for no spark.

uh, have you tried with key on check for power to coil (simple test lamp or VOM) and then grounding the field post (disconnected from dist) momentarily repeatedly. Each release of this short to ground should induce a spark at the coil output.

if it does your coil and it's wiring are presumed OK

rocket science

Mutt and Jeff; thanks for your input. As far as I am concerned, I try to utilize the KISS diagnostics. I must KEEP IT SIMPLE because I am less educated and knowledgeable (STUPID) concerning the ignition system.
draw a SIMPLE wire diagram and I can do the wireing. I won't necessarily understand it all but as long as it works I don't care. 5-4-3-2-1 ignition lift off. gobble

Tomturkey, thanks for bringing up this topic, as this coil business has always confused me also. Used to be you would buy either a 6 volt or a 12 volt coil and that was that. Now you have 12v coils that need a resistor, 12v coils that don't, and just plain 6v coils. It's no wonder that people get confused!

I'm with you----KISS!

Tom good questions here are my answers:


1) "Previous owner converted to alternator."

If so its likely NEGATIVE Ground so the coils input from ign switch should be its + and to distributor should be its -

2) "Shine up points, no spark, test for power to coil good. test light on distributor side of coil, no blinky blinky while cranking."

A test light on the coils output to distributor should flash on (when points open) and off (when points closed) if not shes never gonna fire. If the coils LV primary from + to - is an open circuit (infinity ohms) the coil is BAD

3) "remove wires from coil test resistance with multi-meter, 0 resistance from input terminal to output terminal. Not shorted, but no resistance. Coil is bad-correct?"

Input to output should be around 1.5 ohms if a 6 volt coil and around 3 ohms if a 12 volt coil. If its an open circuit infinity resistance its BAD

4) Wire to input terminal comes from a resistor. Is my coil 6v or 12v? And what do I replace it with?

Typically if it uses an external ballast resistor its a 6 volt coil on a 12 volt system. Again a 6 volt coils has around 1.5 ohms LV primary + to - and around 3 ohms if a 12 volt coil. If its a 12 volt tractor Id use a full true 12 volt coil no ballast required

If all else fails work through my Ignition Troubleshooting Procedure linked below

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T
John Ts Ignition Troubleshooting

First off many cheap VOMs we own are not calibrated so what you get for ohms etc. are ball park figures so common problem with your readings. As for the points you can clean them and many times not do so well enough. Had that HAPPEN to me just the other day and it took a god bit of cleaning to make them work. If good and clean you should be able to turn on the ignition and by hand open and close the points and see a small spark. Not spark the points are not clean enough

?If I check a 3 wire extension cord (hot neutral ground) and I have "continuity" on each wire from end to end is that also "open" but not shorted.? No

?continuity? generally means that there is a conducting path of very low resistance where a conducting path is desired, such as through the individual wires of your extension cord, or the operating wires of a circuit.

?open? means there is no conducting path. ?Open? can be good in that there is no conducting path intended, such as an ?open? or ?off? position on a switch. ?Open? can be bad in that there is no conducting path where one is desired, such as in a broken wire or burned out resistor.

?shorted? means there is a conducting path where one is not desired.

?continuity? and ?shorted? are sometimes used interchangably.

?leaky? means ?an in betweener?, neither fully ?open? nor fully ?shorted? It is a partial or high resistance conducting path where one is not desired such as a partially shorted condenser.

So in your question above the wires from end to end on the extension cord would have ?continuity? or show shorted from end to end, but be ?open? across either end of two separate conductors.

rvirgil_ks, I've read your post more than once. This thick skull of mine tells me I'll need to read it a few more times before it gets thru. The English language is full of words that can have multiple meanings. If a store is open the customers can freely pass thru the door as they wish. If an electrical circuit is open the pathway or door is closed and the customers(electrons?) cannot pass thru. Thank you for your attempt to school me, not sure if this old dog can learn any new tricks. gobble

"no blinky blinky while cranking" does not tell me if the light is on or off.
Makes a big difference.