Farmall 460 coil ballast resistor

Matt1983

Member
I am rewiring my 460 with an original wiring loom and it is wired differently now then it was before. I found the schematics online and I hooked it up following those and now this new wiring loom has a black wire that goes from the ignition switch to an external ballast resistor. On the other side of the resistor is a white wire that comes from the starter (connected to the R post). That wire splits at the resistor and goes to the + side of the coil. In the past there was just a wire from the ignition switch to the + side of the coil.
So now I have it hooked up the way it was originally "supposed to be" and whenever I turn the key on the external ballast resistor starts to smoke and get hot enough to burn you.
I know for a fact that the coil is not original. If it is an internally ballasted coil and I hook it up with the external ballast resistor then would that cause it to burn? Any other ideas as to why it might be burning? If I cant figure it out, Ill just go back to the old way and skip the external resistor. But I don"t want to burn up my coil and points, so I would like some advice first.
Thanks!
 
key on, starter motor not engaged; in this mode you should only have current flow if the points are closed. The R terminal on the starter; when starter is not engaged it should be a dead terminal, no voltage & no continuity to ground, when starter is engaged it should be 12 volts (resister by-pass) for starting
 
What is the R post on the starter? The current may be grounding (short) there & causing the resistor to overheat. That wire should only be live from the starter when cranking, which gives the coil more power than through the resistor. In other words, it by-passes the resistor while cranking.
 
Starter uses about 3 volts from the battery voltage to operate it. Coils were designed to operate on 9 volts. So if the resister is used while the starter is operating, you are left with 6 volts and most likely no ignition spark. Therefore the resister bypass from the starter motor.
 
You got your answer. Just unhook that wire at R terminal of starter solenoid to check. Like they said, that terminal should be an open circuit until starter solenoid engages and then it supplies battery voltage to coil bypassing the resistor for starting. Your next problem is this. If it did not have a resistor before you most likely have a 12 volt coil so running through the resistor will reduce the current flow through coil and provide a weak spark. Look the coil over good to see if it say, 12 volts, or 12 volts with external resistor. Any body with an ohmmeter can check primary winding of coil and tell you what you have. If 2 ohms or less it requires a external resistor. If about 3.5 to 4 ohms it is a true 12 volt coil and you do not want a resistor.
 
Thanks everyone.
That's what I thought Buzz. My points were closed when I was doing all of this but they shouldn't be drawing enough power to burn an external ballast resistor right? Were talking about the resistor becoming HOT within 30 to 45 seconds. I never had an issue like that before.....
I guess I am going to have to test them with the points open. I guess if they continue to burn then there must be a short in the starter on the R side, but it was literally just rebuilt so I hope that's not the case.
Ill report back after I do some more testing.
 
Lots of questions, I will try to sort this out.

NOTE I do NOT have a 460 Wiring Diagram so will have to proceed based on a few assumptions and best guesses SO NO WARRANTY or no complaints or GOTCHAS if this isn't correct!!!!!!!!!!Take it or leave it as you wish, it may be right it may be dead wrong, so there lol


1) It sounds like the 12 volt tractor was set up to use a 6 volt coil plus an external series voltage dropping (12 down to 6) Ballast Resistor.

2) It also sounds like it has a ballast by pass (via a terminal on a starter solenoid) which means ONLY while the starter is cranking the ballast is by passed leaving UNBALLASTED battery voltage to the coil which improves starting especially at colder temps.

3) If its wired wrong such that ign switch output current goes through the ballast direct somehow to ground WITHOUT THE ADDITIONAL SERIES COIL RESISTANCE that would cause the ballast to get very hot!!!!!!!

4) If all is wired correct voltage begins at the IGN switch output,,,,,,when on and running but NOT while cranking, current flows from IGN switch to and through the series ballast, then to the coil. HOWEVER while cranking, current flows from switch (or a starter solenoid terminal thats only hot while cranking, i.e. the starting ballast by pass system) direct to coil by passing the ballast for a short term temporary hotter spark.

5) The above can be accomplished if a wire up from a starter solenoid THAT IS HOT ONLYYYYYYYYY WHILE CRANKING is wired to the ballast output or coil input (same thing electrically).

6) If you use the ballast, and its a 12 down to 6 voltage reducing ballast, YOU NEED A 6 VOLT COIL which may be labeled "6 Volts" or "12 Volts FOR USE with Ballast Resistor" or "12 Volts Requires External Ballast"

7) If you do NOT use the ballast, you need a full true 12 Volt Coil. It may be labeled "12 Volts" or "12 Volts NOT for use with ballast" or "12 Volts NO ballast required" etc

8) If you used a 12 volt coil PLUS still used the series ballast the spark will be weak.

My motto, give a man a fish feed him for a day, teach a man to fish feed him for life" So I gave this detailed explanation in hopes you can now figure it all out BUT NO WARRANTY OR GOTCHAS OR COMPLAINTS as I have no diagram only your information and a few educated best pure guesses.

John T
 
It is normal for the resistor to get hot in the engine is not running, the switch is on, and the points are closed. If it is a new resistor or if any oil or debris happened to get on the resistor it will smoke. Like any other electrical heating element, as then resistor gets hot its resistance goes up and less current will flow through it. It becomes self regulating in that it may get red hot but should not burn out. But like a coil there is no guaranty that they will act as designed. Just don't leave the switch on without the engine running and youl will not have the problem.
 
I ran the tractor today with the resistor in place.
I plan to keep it there until it burns out (if it
does) I agree with you Owen, and I think its fine
and working properly, but I will forget the key on
someday Im sure and Ill burn something out. But I
did figure out that the coil has an internal
resistor so if it burns out it shouldn't burn up my
coil.
Thanks for the help everyone.
 
I'm hoping to start my "new" 460 LP tomorrow; why don't you post some pics of your 460, it is a tractor that you don't see nearly as often as the older letter series tractors...maybe I'll get brave and post mine! Hugh
 
I will try to get some pictures on here when its all put together. I had the engine rebuilt with a 263 crank and fire crater pistons, Im looking forward to seeing what it can do out in the field now with a nice new engine. I also painted the whole tractor with base coat clear coat dark candy apple red. Its really a great color on that tractor. I need to paint the off white pieces still, but after that I will post some pics.
This is a tractor that's been in my family since I was born, and I plan to keep it until my kids can restore it again haha.
Anyway Ill keep you posted.
Thanks again everyone for your help!
 
You say "But I did figure out that the coil has an internal resistor"

If that's true and there actually is a stand alone discrete internal RESISTOR tucked away somewhere inside the can, that's rare for typical old tractor stock type of coil........ I have seen pictures of a very few limited old cars with coils that had a resistor inside the can, but never any old farm tractors.

"so if it burns out it shouldn't burn up my coil"

But if such a resistor (if it actually has one separate inside the can) burns out, it may be hard to get to and repair or salvage the coil, but never say never and never say always or some Billy Bob or Bubba may crawl out and say I GOTCHA LOL

Best wishes, let us know

John T
 
As I said in my initial post/ question, I know that the coil is NOT original. I replaced it several years ago with a high output coil. I had forgotten if it had an internal resistor so I looked up how to test for it, and found that by checking the ohms across both terminals on the coil you can decipher if it has an internal resistor. Mine had 3 ohms of resistance and therefor has an internal resistor.
But I agree with your statement John, about never say never. The minute you do something else goes wrong like my oil pressure problem I just posted about.
 

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