Ih460 wiring ,coil question

Hello guys; Been working on rewiring a shorted out harness. Also replaced the spark plugs, points, condenser, dist cap. Tried to start today. Cranks over good, but no start. I'm getting spark across the points, but looks weak, battery chg good. I tested for spark with a spark plug tester and no spark there. Also tested the primary wire from coil to eng block 3/16in gap and no spark. I called about a coil today and the parts guy asked me if there was a resister in the circuit and there is, but whoever had the tractor before had put in a jumper wire bypassing the resister????????? So is there a difference in coils that has a resister in the circuits? And should I remove the jumper wire. The tractor originally had a generator, but now has an alternator.

A 6v coil or a coil designed to run with a resistor will be 2.5 to 3 ohms or so. A 12v coil will be more like 4 to 5 ohms. Jim

Jim, thanks again for the reply. I was just looking at the forum on 8n and 9n and a couple of guys said that 12v coils can be purchased that doesn't need resistors. Larry

I am building a complete harness for a Farmall 460 gasser at thins time . You have the black wire coming from the key switch to the resistor and a wire from the other terminal to the coil NOW what you need is a white 14ga. wire from the R TERMINAL ON THE STARTER SOLENOID TO THE wire side to the coil . or after the resistor , this way it gets a shot of 12 volts to the points for starting .

thanks tractor vet, I read a post on the 8n forum (Soundguy) and he said that 12 roundcan coils doesn't need resistors. I guess thats why a jumper wire was ran across the resistor thats on there now. I thought my 460 wiring was bad, but sounds like yours was really hacked up. Larry

If a coil is labeled "12 Volts" or "12 Volts NOT for use with Ballast Resistor" or "12 Volts NO Ballast Required" etc on a 12 volt tractor YOU DO NOTTTTTTTTTT USE A BALLAST OR THE SPARK WOULD BE VERY WEAK....

If a coil is labeled "6 Volts" or "12 Volts for use with Ballast Resistor" or "12 Volts requires Ballast" etc on a 12 volt tractor YOU NEED AN EXTERNAL SERIES VOLTAGE DROPPING (12 to 6) BALLAST or else the coil overheats and the points burn rapidly.

Om many 12 volt tractors a 6 volt coil plus an external ballast is used so during cranking the ballast can be bypassed (like an extra I terminal on starter solenoid etc to feed coil direct bypassing ballast while starter is engaged) which helps cold weather starting.

If your ballast was by passed someone likely put on a 12 volt coil (instead of correct 6) and did away with the by pass circuit. It will still work okay as is with poorer starting spark in cold weather as if wired correctly with 6 volt coil and solenoid by pass

Contrary to what many lay persons believe, you most likely will NOT find any discrete stand alone "resistor" hidden away inside the coil can. A 12 volt coil has around 2.5 to under 4 ohms primary resistance while a 6 volt coil has more like 1.25 to 2 ohms

Myself and Bob M and Janicholson have explained this hundreds of times on here do a search for more info if needed

That help?? Any more questions?? See URL link below for more

John T
Coils 101 by John T

The stock Coil for a Farmall is a 6 volt coil and the use of a resistor is used from the factory , on late model 706-806 the ceramic resistor was replaced with a resistor wire . A hot shot wire as i cll it was run from the R terminal on the solenoid to bypass the resistor to give a shot of 12 volts for fast start and hot spark. Now i am not and electrical engineer and maybe my way of doing something are shell we say barnyard engineering i try and follow the book with a few teaks here and there like i do away with the fuse and use self resetting curcit brakers add in C/V relays to take the load off the head light switch when someone want to add more lights then came from the factory since you pushing the factory switch to the max at five lights . I cringe at some of gen to alt. change overs that i have seen , Like running a 65 amp alt thru a 12 ga. wire and like the Farmer wire job that was hacked up on this 460 i am working on at this time . How these guys can sleep at night with something like this setting in a barn full of hay and fifty or so cows down below is unbelievable .

Thanks John T for the info. I'm a shade tree mechanic (I think) with limited electrical expertise, but maybe I can digest all this info.

Thanks for the info,I know many 12 volt tractors use the 6 volt coil and the ballast by pass while cranking, but I had no idea WHICH MODELS. The R or I (what Fords used) terminal on the starter solenoid is a terminal thats hot ONLY while the starter is engaged and it connects direct to the coil input so it sees unballasted battery voltage ONLY while cranking fOR TH hotter starting spark, its a good system if all is well...

Fun chat

John T

John T, I read all your info on coils. So I had a little time this evening to go out to the tractor shed and look at the wiring again. Haven't had much time to work on it lately. When looking at the coil it wasn't stamped 6volts or 12 that I could see, very rusty and old looking (like me). I did see some wording that said,use with external resistor and there was a #27291 stamped on it. Since the tractor has 12volt system should i ask for a 6volt or 12volt coil to install on it? Thanks Larry

"I did see some wording that said, use with external resistor"

If it says that my best "guess" is it means just what it says i.e. it requires the resistor or else it will overheat....Id try that coil WITH the unshunted external ballast n see what happens.

"Since the tractor has 12 volt system should I ask for a 6 volt or 12 volt coil to install on it?"

You can EITHER use a 6 volt coil PLUS the external series voltage dropping (12 to 6) working ballast orrrrrrrrrrrr a 12 volt coil with no ballast required. However to utilize the ballast by pass system for improved cold starting you would need the 6 volt coil plus a good ballast. Id be tempted to just use a new full 12 volt coil (NO ballast required) and do away with any ballast or by pass circuit headaches...

John T

6V or 12V... Well, do you want it "original" or do you want to simplify the system?

If you want original, get a 6V coil, remove the jumper wire from the resistor, and set up the "boost" circuit like Tractor Vet described earlier.

If you want simple, get a 12V coil, and completely REMOVE the ballast resistor.

Tractor Vet, (I'm getting my electrical course on this webb site THANKS TO ALL FOR THE HELP) you indicated someone had installed a 65 amp alt with a 12 ga. wire on a tractor (not good). So I thought I better ask you. On my ih460 the alt was bad, had it tested. The alt had come off a 73 chev pu, it was marked what it came off by someone. Soooooooo I had one that came off a 75 pontiac 400cu in. that tested good and put it on the tractor. Now i do not know what amps it is pushing thru the wires and what size alt would that tractor use? DON"T WANT TO BURN DOWN THE SHED Larry