49 8n ignition resistor burning up

RRSPRINGS

New User
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
 
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
Which distributor, front or side mount? Stand-alone coil or original one on the distributor? A high amperage draw through the resistor would burn it up. I would start by checking for a short in the primary circuit between the coil and the points. Bad wire, bad insulator, something around the points contacting the points and distributor base could create a short circuit.
 
Which distributor, front or side mount? Stand-alone coil or original one on the distributor? A high amperage draw through the resistor would burn it up. I would start by checking for a short in the primary circuit between the coil and the points. Bad wire, bad insulator, something around the points contacting the points and distributor base could create a short circuit.
It’s a front mount distributor with with an 12v coil sitting on top of the distributor.
 
Jim, you seem off point to me. If I am understanding what you said “a short in the primary circuit between the coil and the points” this would kill the engine. I guess he is not saying if it is running when this happens.

Hello RR, welcome to YT! Is this the resistor on the junction block up on the dash? The only thing that should be on that circuit pulling a load through the resistor is the coil. My guess is some other circuit and current are passing through it due to incorrectly connection/wiring is wrong. Same applies no matter where the resistor is. I’ll attach some wiring diagrams. Ford N wiring diagrams
 
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Jim, you seem off point to me. If I am understanding what you said “a short in the primary circuit between the coil and the points” this would kill the engine. I guess he is not saying if it is running when this happens.

Hello RR, welcome to YT! Is this the resistor on the junction block up on the dash? The only thing that should be on that circuit pulling a load through the resistor is the coil. My guess is some other circuit and current are passing through it due to incorrectly connection/wiring is wrong. Same applies no matter where the resistor is. I’ll attach some wiring diagrams. Ford N wiring diagrams
(PS prepare for the onslaught of info when Tim D. sees your post)
Yes it’s the resistor on the junction block at the dash. I’ll double check the wiring tomorrow.
 
Jim, you seem off point to me. If I am understanding what you said “a short in the primary circuit between the coil and the points” this would kill the engine. I guess he is not saying if it is running when this happens.

Hello RR, welcome to YT! Is this the resistor on the junction block up on the dash? The only thing that should be on that circuit pulling a load through the resistor is the coil. My guess is some other circuit and current are passing through it due to incorrectly connection/wiring is wrong. Same applies no matter where the resistor is. I’ll attach some wiring diagrams. Ford N wiring diagrams
(PS prepare for the onslaught of info when Tim D. sees your post)
True, if it is the original resistor on the terminal block behind the dash, it could be overloaded by something incorrectly wired into the circuit, as well as a chafed/shorted wire anywhere between the resistor and points. He posted. "After running for a short time the resistor starts glowing red and catches fire." I assumed burning up the resistor in flames twice and usually burning up the coil would kill the engine, if it was running. He rewired it, so a question might be how soon after being rewired did this issue start?

RR, I see you replied you are talking about the original resistor mounted to the terminal block on the back side of the dash, do you have only one wire on each of the terminals for the resistor? One from the switch and one going to the coil (only)? All others should be on the junction terminal centered below the resistor. Did you install an alternator as part of this? If you did, what type and where did you connect its output wire?
 
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

Your wiring is incorrect. You do not add the external 1.5 OHM ceramic Resistor to the coil circuit if you have a 12V coil. Only add it in if using your 6V Coil. So you're using a front mount distributor. Is the OEM BALLAST RESISTOR in the circuit? Using a DELCO 10-SI 1-Wire or 3-Wire ALT? Got a belt tensioner attached? Are the GEN and VR removed from the circuit? Is the Starter Motor a 3-wire unit with the Relay (SOLENOID) and wired correctly? Is battery 12V NEG GRN with correct cables? SEE PICTOGRAMS for wiring. What does the AMMETER show at start up?

Tim Daley (MI)


 

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I am not a fan of Tim’s (JMOR’s) pictogram that shows the blue wire coming off the ammeter in the lower right. This configuration, will not register any loads on the electrical system like ignition or lights, only the positive amperes the alternator is charging.
 
I am not a fan of Tim’s (JMOR’s) pictogram that shows the blue wire coming off the ammeter in the lower right. This configuration, will not register any loads on the electrical system like ignition or lights, only the positive amperes the alternator is charging.
I'm mot a fan of that configuration, either, but folks ask for such configurations and I accommodate. Choose the one you like, ask me to draw one, and/or draw your own. I have drawn & have on file over 75 similar diagrams, so there is a lot of them floating about to choose from. I do favor a net reading ammeter. I think Atlantic conversion kits were the instigator of those "wrong" ammeter connections.
 
Yes it’s the resistor on the junction block at the dash. I’ll double check the wiring tomorrow.
Just a FYI
I have seen aftermarket resistor/junction blocks that the screw heads are not countersunk far enough and can ground out on the dash. Those I have seen were Sparex brand.
 
All,

Attached is how the tractor is currently wired.
I assume by Gen and VR you mean the alternator and yes they were taken out of the circuit. The alternator is a one wire alternator.
If referring to ballast resistor like the one attached there’s never been one on the tractor. The starter is the one attached purchased from yesterday’s tractor.
 

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All,

Attached is how the tractor is currently wired.
I assume by Gen and VR you mean the alternator and yes they were taken out of the circuit. The alternator is a one wire alternator.
If referring to ballast resistor like the one attached there’s never been one on the tractor. The starter is the one attached purchased from yesterday’s tractor.
Not sure what type I’ll have to check, also there is a belt tensior installed
 
In post 5 he said it is the resistor on the junction block at the dash.
Ditto !There is NO junction block on the front mount BUT guys use terms they don't know is correct. May be calling the 12250 Ballast Resistor a 'junction block'. He also says he is "burning up the ceramic resistor" but that could be the OEM 9N-12250 Ballast Resistor or the aftermarket 1.5 OHM External Resistor used with a 6V Coil. Again unclear. When I see/read "ceramic" I am thinking the aftermarket external part. When I see/read "junction block" I think p/n 8NNN-14448, used with all side mount units when the change was made in 1950, and when the 12250 Ballast Resistor was obsoleted. To clarify:

9N-12250 - OEM Ballast Resistor, used '39-'50 only with front mount distributor.

8NNN-14448 - Junction Block, used only with side mount distributor, when the 12250 Ballast Resistor was obsoleted.

8N-10306 - External Inline 1.6 OHM Resistor; used only with a 6V Coil in a 12V system.


Tim Daley (MI)

FWIW & FYI : The OEM 9N-12250 Ballast Resistor was originally ceramic and IT WILL GET HOT! It can be red glowing. When you install a new resistor, at first power-up it will get hot and smoke a bit. Don't panic and think you've freid something -this is normal. Burning up a Coil, 6V or 12V, is NOT normal so suspect your wiring is incorrect somewhere in the system. How did you verify the coil was "'burning up"?

Tim Daley (MI)
 

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In post 5 he said it is the resistor on the junction block at the dash.
Ditto !There is NO junction block on the front mount BUT guys use terms they don't know is correct. May be calling the 12250 Ballast Resistor a 'junction block'. He also says he is "burning up the ceramic resistor" but that could be the OEM 9N-12250 Ballast Resistor or the aftermarket 1.5 OHM External Resistor used with a 6V Coil. Again unclear. When I see/read "ceramic" I am thinking the aftermarket external part. When I see/read "junction block" I think p/n 8NNN-14448, used with all side mount units when the change was made in 1950, and when the 12250 Ballast Resistor was obsoleted. To clarify:

9N-12250 - OEM Ballast Resistor, used '39-'50 only with front mount distributor.

8NNN-14448 - Junction Block, used only with side mount distributor, when the 12250 Ballast Resistor was obsoleted.

8N-10306 - External Inline 1.6 OHM Resistor; used only with a 6V Coil in a 12V system.


Tim Daley (MI)

FWIW & FYI : The OEM 9N-12250 Ballast Resistor was originally ceramic and IT WILL GET HOT! It can be red glowing. When you install a new resistor, at first power-up it will get hot and smoke a bit. Don't panic and think you've freid something -this is normal. Burning up a Coil, 6V or 12V, is NOT normal so suspect your wiring is incorrect somewhere in the system. How did you verify the coil was "'burning up"? How do yiou plan to 'test'

Tim Daley (MI)
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
FWIW & FYI : The OEM 9N-12250 Ballast Resistor was originally ceramic and IT WILL GET HOT! It can be red glowing. When you install a new resistor, at first power-up it will get hot and smoke a bit. Don't panic and think you've fried something -this is normal. Burning up a Coil, 6V or 12V, is NOT normal, and 'catching fire' is certainly not normal which indicates a bad wiring issue. I suspect your wiring is incorrect somewhere in the system. How did you verify the coil was "'burning up"? How did you plan to "test the circuit for shorts" and where & how to look at voltages? Many just start probing their VOM without knowing exactly where to test and what to look for.

You need to:
1. Disconnect Battery and Lights. Lights were never a factory feature and many are wired incorrectly, often root cause for shorts.
2. Go thru entire wiring system with a VOM set to Continuity, and do not use an idiot test light. Use the correct wiring PICTOGRAM by JMOR.
3. Verify all the wiring is correct for the Front Mount 8N; do you have the correct GENERATOR and belt tensioner, VOLTAGE REGULATOR, and START MOTOR? All wiring harness must be right.
4. Lastly, the front mount distributor is often the root cause for non-starting. If not tune-up, timed, and tested correctly then mounted correctly, it will be a problem.

Your local ALT/GEN shop can bench test Battery, GEN, VR, and Starter Motor, usually at no charge (pun intended)

Tim Daley (MI)
 

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Ditto !There is NO junction block on the front mount BUT guys use terms they don't know is correct. May be calling the 12250 Ballast Resistor a 'junction block'. He also says he is "burning up the ceramic resistor" but that could be the OEM 9N-12250 Ballast Resistor or the aftermarket 1.5 OHM External Resistor used with a 6V Coil. Again unclear. When I see/read "ceramic" I am thinking the aftermarket external part. When I see/read "junction block" I think p/n 8NNN-14448, used with all side mount units when the change was made in 1950, and when the 12250 Ballast Resistor was obsoleted. To clarify:

9N-12250 - OEM Ballast Resistor, used '39-'50 only with front mount distributor.

8NNN-14448 - Junction Block, used only with side mount distributor, when the 12250 Ballast Resistor was obsoleted.

8N-10306 - External Inline 1.6 OHM Resistor; used only with a 6V Coil in a 12V system.


Tim Daley (MI)

FWIW & FYI : The OEM 9N-22510 Ballast Resistor was originally ceramic and IT WILL GET HOT! It can be red glowing. When you install a new resistor, at first power-up it will get hot and smoke a bit. Don't panic and think you've freid something -this is normal. Burning up a Coil, 6V or 12V, is NOT normal so suspect your wiring is incorrect somewhere in the system. How did you verify the coil was "'burning up"? How do yiou plan to 'test'

Tim Daley (MI)

FWIW & FYI : The OEM 9N-12250 Ballast Resistor was originally ceramic and IT WILL GET HOT! It can be red glowing. When you install a new resistor, at first power-up it will get hot and smoke a bit. Don't panic and think you've fried something -this is normal. Burning up a Coil, 6V or 12V, is NOT normal, and 'catching fire' is certainly not normal which indicates a bad wiring issue. I suspect your wiring is incorrect somewhere in the system. How did you verify the coil was "'burning up"? How did you plan to "test the circuit for shorts" and where & how to look at voltages? Many just start probing their VOM without knowing exactly where to test and what to look for.

You need to:
1. Disconnect Battery and Lights. Lights were never a factory feature and many are wired incorrectly, often root cause for shorts.
2. Go thru entire wiring system with a VOM set to Continuity, and do not use an idiot test light. Use the correct wiring PICTOGRAM by JMOR.
3. Verify all the wiring is correct for the Front Mount 8N; do you have the correct GENERATOR and belt tensioner, VOLTAGE REGULATOR, and START MOTOR? All wiring harness must be right.
4. Lastly, the front mount distributor is often the root cause for non-starting. If not tune-up, timed, and tested correctly then mounted correctly, it will be a problem.

Your local ALT/GEN shop can bench test Battery, GEN, VR, and Starter Motor, usually at no charge (pun intended)

Tim Daley (MI)
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?
 
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?
OK, Jim. fair enough but me, like I said, when I hear "junction block" I am thinking the later FORD junction block used on side mounts. I suppose technically you can call the Ballast Resistor a junction block. I'm just used to keeping things clearer.

Respectfully,
Tim
 

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