49 8n ignition resistor burning up

I have a 49 8n that has recently developed an issue of burning up the ceramic ignition resistor. The tractor has been converted to 12v and new wiring harness installed earlier this year. After running for a short time the resistor starts glowing red and catches fire. It’s happened twice so far and usually also ends of burning up the 12v ignition coil as well. I haven’t had time yet to try and test for a short circuit, but also I’m limited to how long the resistor lasts to check voltages. Anyone have something similar happen?

Thanks
Rob
You say recently developed this issue. I take it, it ran okay earlier in the year? That would eliminate wrong wiring I would think. If the ballast resister was shorted to the dash, I can't see it burning up the coil either. I am confused though, as the photos you posted show an in line ceramic resister which you don't need if you have a 12 volt coil.
You don't have time to take voltage measurements, but you can check for false ground at different points with the key off.
 
You say recently developed this issue. I take it, it ran okay earlier in the year? That would eliminate wrong wiring I would think. If the ballast resister was shorted to the dash, I can't see it burning up the coil either. I am confused though, as the photos you posted show an in line ceramic resister which you don't need if you have a 12 volt coil.
You don't have time to take voltage measurements, but you can check for false ground at different points with the key off.
Regarding the resistor, read post #14. The tractor never had one, he posted the picture to be sure what Tim was talking about.
 
So hopefully I can clear up some of the confusion with the parts in question. Attached is the most recent resistor to burn up. I have noticed that each time this has burned and is replaced the tractor won’t start unless I put a new coil pack on. I probably won’t get any time for testing until the weekend.
 

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You say recently developed this issue. I take it, it ran okay earlier in the year? That would eliminate wrong wiring I would think. If the ballast resister was shorted to the dash, I can't see it burning up the coil either. I am confused though, as the photos you posted show an in line ceramic resister which you don't need if you have a 12 volt coil.
You don't have time to take voltage measurements, but you can check for false ground at different points with the key off.
Yes it ran earlier in the year after I had a friends dad take look at and tune it up.
 
So hopefully I can clear up some of the confusion with the parts in question. Attached is the most recent resistor to burn up. I have noticed that each time this has burned and is replaced the tractor won’t start unless I put a new coil pack on. I probably won’t get any time for testing until the weekend.
This one still functioned AND had proper resistance value
 
So hopefully I can clear up some of the confusion with the parts in question. Attached is the most recent resistor to burn up. I have noticed that each time this has burned and is replaced the tractor won’t start unless I put a new coil pack on. I probably won’t get any time for testing until the weekend.
@RRSPRINGS in regards to reply 23. So turn that around and show the back side. That is what Dean in reply 12 is talking about if the proper counter sinking has been made for the posts in it. Which means they may be shorting out to the metal they are mounted on.
 
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Tim,

Many, me included, would call/consider the 9N-12250 OEM Ballast Resistor the "original resistor on a junction block" considering the third terminal on the block (that the 9N-12250 resistor is mounted on) is used as a junction for multiple wires unrelated to the resistor terminals. Doesn't that description identify which one he is looking at? Most are not as well versed as you are in the parts to know that the resistor and the block it is mounted on are two separate parts. Part numbers aside, what do you suggest that assembly be called?

He clarified there is no additional ceramic ballast resistor in the system, see post #14

It was established earlier in the thread that the generator and regulator were removed and replaced with a one wire alternator, with a belt tensioner. see posts #14 and 15

No lights are shown in the sketch he made of his system, see post #14

How about some direct on point help for the 12-volt system he has described and shown, as well as help with his problem, not a bunch of nit-picking names and part numbers as well as repeating info related to the old 6-volt system, which he removed, which adds confusion?

I believe you have repeatedly said the OEM resistor must remain even if converted to 12 volts. If the 12-volt coil ohms out at 3 to 4 ohms why would that resistor not be removed, as a ballast resistor would be when changing a unit that used a 6-volt can coil with a ballast resistor to a true 12-volt coil, wound and having internal resistance to provide the 3 to 4 ohm resistance?
Well Mr. Jim, we shall agree to disagree I guess, but I learned a long time ago how to read and decipher the MPC's with part numbers and descriptions so have always called the 9N-12250 the "Resistor Assembly (Ignition Coil)" as it is listed and never a 'Junction Block'. Additionally, the 8NNN-14448 is listed as the "BLOCK ASSY. (Electric Wiring Junction)" and came later after 1950 as you know. A lot of guys also assume the junction block is also a resistor - it ain't, and that only perpetuates the wrong info getting out there. I prefer to be clear, direct, and precise. So it is what it is bro.

Your Mileage May Vary,
Tim Daley (MI)
 

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Well Mr. Jim, we shall agree to disagree I guess, but I learned a long time ago how to read and decipher the MPC's with part numbers and descriptions so have always called the 9N-12250 the "Resistor Assembly (Ignition Coil)" as it is listed and never a 'Junction Block'. Additionally, the 8NNN-14448 is listed as the "BLOCK ASSY. (Electric Wiring Junction)" and came later after 1950 as you know. A lot of guys also assume the junction block is also a resistor - it ain't, and that only perpetuates the wrong info getting out there. I prefer to be clear, direct, and precise. So it is what it is bro.

Your Mileage May Vary,
Tim Daley (MI)
Tim,

You posted, "I learned a long time ago how to read and decipher the MPC's with part numbers and descriptions so have always called the 9N-12250 the "Resistor Assembly (Ignition Coil)" as it is listed and never a 'Junction Block".

It appears the MPC information, you posted here, shows 9N-12250-B as Resistor assembly (Ignition Coil). I do not see the part number 9N12250 shown in that page of the MPC. If I search the Dennis Carpenter catalog, which you often promote people to get and use, the 9N12250 is shown as:

Coil Resistor
- replacement type
- no mounting plate

Online searches for 9N12250 turn up the bare resistor, no mounting block, for most results, not the resistor assembly.


Many people now use the online parts catalogs, as they don't have a copy of the MPC. Then there is the reality many of those MPC numbers have been superseded, as was found for the front seal on a PTO shaft being discussed by others and you, the other day. The current part number for the resistor assembly with mounting block is A8NN12250B, using the online NH/Ford (get over it, New Holland bought them) catalog. The Dennis Carpenter catalog uses A8NN numbers for all the resistor and block assemblies, not 9N12250 or 9N12250-B.

My description may not match the MPC description, or your terms. I am trying to describe what the person new to the tractor's issue is seeing and work them through things. I have no issue with you giving MPC part numbers, etc. but often if you would add more info more at the level of a person trying to learn, to explain these things to them, it could help them. Also giving them the current part numbers to look for, rather than telling them they need to get an outdated MPC. By the same token if the resistor is mounted on an insulated block having a third terminal separate from the resistor circuit screws, where several wires are joined for a power connection, why do I need a lecture about it not being a junction block just because a later model has a different part specifically called a junction block. Many other pieces of equipment in this world I have worked on have junction blocks of various types. Sorry but junction block is not a name, or term, specific to just one 9N-part number.

We can go back and forth on these little details forever and help no one. Post the numbers and use the names you want. I acknowledge the info specific to these tractors you have acquired over the years and respect you sharing it. One thing I will say is that if one is working on a tractor that has been converted to 12-volts, help them with their 12-volt problem, not expound on why it should be 6 volts, time for that discussion passed when the conversion was done, unless they are asking for help doing a full restoration to bring it back to original. You will have to tolerate my ignorance and approach. I will continue to describe things as best I can by using common names/terms for the related part numbers, and trying to explain the purpose they serve, when I think it is helping the person understand. It worked training new people on mechanical projects before I retired, and I think it will help here. I am sure I have made, and will make more, mistakes along the way, just as you have and will.

Hope you are doing well health wise.

Best regards
Jim
 
Tim,

You posted, "I learned a long time ago how to read and decipher the MPC's with part numbers and descriptions so have always called the 9N-12250 the "Resistor Assembly (Ignition Coil)" as it is listed and never a 'Junction Block".

It appears the MPC information, you posted here, shows 9N-12250-B as Resistor assembly (Ignition Coil). I do not see the part number 9N12250 shown in that page of the MPC. If I search the Dennis Carpenter catalog, which you often promote people to get and use, the 9N12250 is shown as:

Coil Resistor
- replacement type
- no mounting plate

Online searches for 9N12250 turn up the bare resistor, no mounting block, for most results, not the resistor assembly.


Many people now use the online parts catalogs, as they don't have a copy of the MPC. Then there is the reality many of those MPC numbers have been superseded, as was found for the front seal on a PTO shaft being discussed by others and you, the other day. The current part number for the resistor assembly with mounting block is A8NN12250B, using the online NH/Ford (get over it, New Holland bought them) catalog. The Dennis Carpenter catalog uses A8NN numbers for all the resistor and block assemblies, not 9N12250 or 9N12250-B.

My description may not match the MPC description, or your terms. I am trying to describe what the person new to the tractor's issue is seeing and work them through things. I have no issue with you giving MPC part numbers, etc. but often if you would add more info more at the level of a person trying to learn, to explain these things to them, it could help them. Also giving them the current part numbers to look for, rather than telling them they need to get an outdated MPC. By the same token if the resistor is mounted on an insulated block having a third terminal separate from the resistor circuit screws, where several wires are joined for a power connection, why do I need a lecture about it not being a junction block just because a later model has a different part specifically called a junction block. Many other pieces of equipment in this world I have worked on have junction blocks of various types. Sorry but junction block is not a name, or term, specific to just one 9N-part number.

We can go back and forth on these little details forever and help no one. Post the numbers and use the names you want. I acknowledge the info specific to these tractors you have acquired over the years and respect you sharing it. One thing I will say is that if one is working on a tractor that has been converted to 12-volts, help them with their 12-volt problem, not expound on why it should be 6 volts, time for that discussion passed when the conversion was done, unless they are asking for help doing a full restoration to bring it back to original. You will have to tolerate my ignorance and approach. I will continue to describe things as best I can by using common names/terms for the related part numbers, and trying to explain the purpose they serve, when I think it is helping the person understand. It worked training new people on mechanical projects before I retired, and I think it will help here. I am sure I have made, and will make more, mistakes along the way, just as you have and will.

Hope you are doing well health wise.

Best regards
Jim
You guys should expand you quibbling to mounting screw sizes/hole sizes while you are at it. :) Might help poster with "burning" up problem. I'm just riding along for entertainment at this point.
 
@RRSPRINGS in regards to reply 23. So turn that around and show the back side. That is what Dean in reply 12 is talking about if the proper counter sinking has been made for the posts in it. Which means they may be shorting out to the metal they are mounted on.
I checked the back side of each screw and the metal it was mounted on for any indications of arcing and didn’t see any. I am going to go ahead and take a countersink bit and drill them a little deeper just to be sure.
 
Tim,

You posted, "I learned a long time ago how to read and decipher the MPC's with part numbers and descriptions so have always called the 9N-12250 the "Resistor Assembly (Ignition Coil)" as it is listed and never a 'Junction Block".

It appears the MPC information, you posted here, shows 9N-12250-B as Resistor assembly (Ignition Coil). I do not see the part number 9N12250 shown in that page of the MPC. If I search the Dennis Carpenter catalog, which you often promote people to get and use, the 9N12250 is shown as:

Coil Resistor
- replacement type
- no mounting plate

Online searches for 9N12250 turn up the bare resistor, no mounting block, for most results, not the resistor assembly.


Many people now use the online parts catalogs, as they don't have a copy of the MPC. Then there is the reality many of those MPC numbers have been superseded, as was found for the front seal on a PTO shaft being discussed by others and you, the other day. The current part number for the resistor assembly with mounting block is A8NN12250B, using the online NH/Ford (get over it, New Holland bought them) catalog. The Dennis Carpenter catalog uses A8NN numbers for all the resistor and block assemblies, not 9N12250 or 9N12250-B.

My description may not match the MPC description, or your terms. I am trying to describe what the person new to the tractor's issue is seeing and work them through things. I have no issue with you giving MPC part numbers, etc. but often if you would add more info more at the level of a person trying to learn, to explain these things to them, it could help them. Also giving them the current part numbers to look for, rather than telling them they need to get an outdated MPC. By the same token if the resistor is mounted on an insulated block having a third terminal separate from the resistor circuit screws, where several wires are joined for a power connection, why do I need a lecture about it not being a junction block just because a later model has a different part specifically called a junction block. Many other pieces of equipment in this world I have worked on have junction blocks of various types. Sorry but junction block is not a name, or term, specific to just one 9N-part number.

We can go back and forth on these little details forever and help no one. Post the numbers and use the names you want. I acknowledge the info specific to these tractors you have acquired over the years and respect you sharing it. One thing I will say is that if one is working on a tractor that has been converted to 12-volts, help them with their 12-volt problem, not expound on why it should be 6 volts, time for that discussion passed when the conversion was done, unless they are asking for help doing a full restoration to bring it back to original. You will have to tolerate my ignorance and approach. I will continue to describe things as best I can by using common names/terms for the related part numbers, and trying to explain the purpose they serve, when I think it is helping the person understand. It worked training new people on mechanical projects before I retired, and I think it will help here. I am sure I have made, and will make more, mistakes along the way, just as you have and will.

Hope you are doing well health wise.

Best regards
Jim
1940 MPC lists part as 9N-12250-B, RESISTOR. Carpenter shows as a replacement type. P/N 18-12250 is exact ceramic part and metal base but no Bakelite block, was used on prior vehicles REF my 1937-1942 sketches.

Tim


https://www dennis -carpenter com/trucks/engine/ignition-amp-timing/18-12250-ignition-coil-resistor-origin

delete spaces and add DOT B4 com
 
Where are you getting your coils from? Are you sure they are 12 volt coils? The next one you get, measure the resistance between the pig tail and the top of the coil. A 12 volt coil should be around 2-3 ohms where a 6 volt will be around 1 ohm.
I still think that if the resister assembly was shorting to the dash you wouldn't burn up the coil. Electrons take the easiest path to ground.
 
Where are you getting your coils from? Are you sure they are 12 volt coils? The next one you get, measure the resistance between the pig tail and the top of the coil. A 12 volt coil should be around 2-3 ohms where a 6 volt will be around 1 ohm.
I still think that if the resister assembly was shorting to the dash you wouldn't burn up the coil. Electrons take the easiest path to ground.
I was planning on brining my multimeter home from work this weekend to do some testing. I have several coils that I will double check. Thanks.
 

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