My 9n tractor 12 volt conversion

I did the 12 volt conversion on my 1950 9n. It would not fire with resistor number 2 but runs fine without it. I am worried about the coil so only ran it for a moment. Puzzled. Any thoughts? Thanks. Iven

Check to make sure coil doesn't have an internal resistor! If it has one no need for external one.

no such thing as an internal resistor.. I challange you to find a modern mass produced coil with an internal resistive element, vs instead, just a primary wound with correct length and diamater wire to meet 'target' impedance.

9n were made from 1939 thru 1941 with 2n as model year 1942 thru 1946, 8n started with model year 47 and continued thru 52.

you could get a frontmount N in an early 8n, and 9n/2n were only front mount.

you MAY have a 1950 8n chassis with a 9n engine.. but it is not a 1950 9n.. etc.

that said.

you did a 12v conversion.. it should have an oem resistor on the back of the dash. if the kit provider also gave you a 2.5 ohm '12v' square coil, then you can run that coil with the oem ballast resistor and be fine. The additional ceramic resistor would be used with the oem ballast resistor if you were keeping the oem 1ish ohm '6v' coil.

So what wording on the coil should he look for that would tell him whether or not he needs an external resistor?

Good Luck, I've also told em that for years, but that old wives tale isn't going away lol. Sure, there were a very very few very older cars that had an actual "resistor" in a compartment in the can (I had a picture once) BUT NO TYPICAL TRACTOR COILS (Circa 30's through 70's) I've ever seen had a discrete stand alone "resistor" hidden away inside the can. Like you, do an X Ray or disect one, betcha you wont find a "resistor" in there!!! Wire, not being a perfect conductor, has some "resistance" but its NOT called a "resistor". Similar, a resistor conducts current, but its NOT called wire lol

Its an Urban Legend and by golly its here to stay lol

John T

many round can coils today will say something like, 'needs no external resistance' and then list, for instance, 12v. a napa ic14sb ( round can ) coil is printed like this. this tells you it is a native coil for a 12v application with no series primary resistance.

on the other hand.. some companies get a lil deceptive, kinda... they will print '12v' then in flyspec printing say 'with serial resistance' telling you it is basically a '6v' or '8v' coil that needs serial primary resistance to function in a 12v application.

Many do that if it is in a bypass ignition system ( an N does not have a bypass system .. close.. but no cigar ). in a bypass system, the 6v coil lives in series with a resistor on a 12v system, during startng when battery voltage is taxed, the resistor is out of circuit and full 'available' bat volts hits the coil, making as hot as possible sparks with respect to air gap.. a N uses a ballast resistor with a thermal coeficient. when it is cold, it is low resistance... thus giving some extra sparkies.. it quicklyu heats up as current flows like the wire in a toaster, and the resistance goes up, lowering the current. i won't get into the electronics definition of voltage drop and current flow.. but suffice it to say it works according to ohms law among others.

now.. on the 9n.. they don't have those nifty round coils.. they have square coils... the originals were more like a 4.5v coil in a 6v system, which is why a resistro was needed. those original coils had a primary impedance of about 1 ohm 'or so' I have measured units from .9 to 1.25 depending on age and country of origin. the 12v application square coils typically measure out to about 2.5 ohms.. though again. i have seen rare variants down to 2.0 ohms.. and some as high as 2.8... 2.5 is the commonly supplied chinese origin one.... if you are real lucky, the coil may say what it's primary resistance is. a square cold sold as 12v can be assumed to be a 2.5 ohm coil... add that tot he hot ballast resistor that stabilizes around a half an ohm or a lil more.. and you have a safe primary current.

Mike, until Soundguy gets back, I haven't seen them all lol but for the most part a coil labeled:


"12 Volts" or "12 Volts NOT for use with External Ballast" or "12 Volts no Ballast required" ARE DESIGNED FOR 12 VOLT USE

On the other hand if labeled:

"6 Volts" or "12 Volts for use with Ballast Resistor" or "12 Volts, requires Ballast"

If used on a 12 volt tractor they mean just what they say A BALLAST IS REQUIRED

John T

it's a darn shame is what it is...

in this day and age where everybody practically owns and can operate a computer or phone ( computer! ) to not be able to understand a simple math equation of E=IR and solve for it knowing the E variable, and knowing the target I variable, thus telling you what R needs to be close to.. then simply referencing hte manufacturer info on the coil or measuring it....

sad...

Hey, I'm pretty handy on a Computer, but give me a smart phone (I have an old dumb flip one I can barely use) or a digital camera and despite being an electrical engineer, I'm out to lunch lol. I'm of the fifties ANALOG generation NOT the digital generation. I still cling to my old Simpson 260 Analog meter (along with Guns and God as the president criticized)

A recent study showed if you give a remote to a 6 yr old (of the digital generation) they can figure it out faster then a college student as they are open minded and dont have any pre conceived problem solving notions. I cant operate a smart phone or tablet etc., but my 6 yr old granddaughter (who couldn't even read the instructions) can figure them out grrrrrrrrrr

Getting old John T

i agree. I like analog. I used to have a walgreens tube tester ( the big display kind that you walked up and plugged yer tube in.. etc.

I urge the "sparkies" here to contact whomever makes the replacement coils for JD pony motors and tell them how to wind some more wire in there and start making the coils to work on 12 volt.

Mike, That's just a 6 volt system and that little pony motor spins really fast and she starts fine even at cold temps at only 6 volts, I don't really see a need to make the coils 12 volt do you????????

John T

Plenty of reasons to switch over to 12V one of them being hopes of the coils not being so sensitive.

If you got an old worn one and convert it over to 4 car coils boy it sure makes them run !

2n,9n,8n all work fine for me on 6 volts too but the market sure has catered to converting them over to 12V

Fer sure, a buddy of mine used 4 car coils but that can be hard on points if all isn't ballasted correct (which Billy Bob out there has no idea how to do). However if those Wico's are maintained she fires fine and if all else is well the 6 volts spins the ponys plenty fast while 12 volts on them is rough on starter drives, its just too much. Sure there are times where a 12 volt conversion is okay, but I think its a bit much to butcher up a good 6 volt pony system. But to each their own, your money your tractor, but converting a pony tractor to 12 volts isn't for me but I do agree the lights are much better!!!

What some guys have done when using the new better coils is to by pass the ballast resistor which increases spark energy no 12 volts required and they start and perform fine.

Fun chat

John T

I just bought the 9N kit from this site. they included a 12 volt coil and an additional resistor shown on the enclosed print as in line with the coil. No fire. Removed the new resistor and it ran great. After a little bit I checked the coil temp with my hand and it wasn't even warm. Its been running great. The kit was confusing, and I have done several using junk and jmor instructions.