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FBOP

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I posted here earlier about the trouble I was having with my 8N not having spark. I was given some pointers and in checking everything I found that my new coil was bad. I replace the coil, ignition, resistors, spark plugs, spark plug wires, distributor cap, points and condenser and it fired right up and ran better than it has in years! A wonder what a complete tune up will do. Everything was fine until today, after mowing a couple of acres behind the neighbor's, the tractor wouldn't restart to go home. We checked for spark and I was back to nothing at the plug! After I got home my neighbor called and said he had rewired the system using only 1 resistor (12 volt conversion) and it started just fine. Doesn't the 12 volt conversion require two resistors? What am I doing wrong?
 
(quoted from post at 20:37:25 08/27/15)After I got home my neighbor called and said he had rewired the system using only 1 resistor (12 volt conversion) and it started just fine. Doesn't the 12 volt conversion require two resistors?

It depends.

If you have a 12 V coil, you only need the original ballast resistor.

If you have a 6 V coil, you need the ballast resistor and an additional resistor to drop prevent the 6 V coil from melting.
 
(quoted from post at 12:34:16 08/28/15)
(quoted from post at 20:37:25 08/27/15)After I got home my neighbor called and said he had rewired the system using only 1 resistor (12 volt conversion) and it started just fine. Doesn't the 12 volt conversion require two resistors?

It depends.

If you have a 12 V coil, you only need the original ballast resistor.

If you have a 6 V coil, you need the ballast resistor and an additional resistor to drop prevent the 6 V coil from melting.

OK, I think I've got it fixed now. Some how I got it in my head that I needed two resistors with the 12 v coil. We just bypassed one of the two I now have installed and it seems to be working fine again. Thanks!
 
I read tip #30, but I still have a question. My engine was rebuilt at a tractor shop that specializes in Ford tractors, so they do a lot of conversions. I have a 9N (therefore front mount)12V that does not have the original ballast resistor. My question is couldn't you replace both resistors with one resistor if it is the correct resistor? Do you know if they make the "correct" resistor to replace the 2 with 1? If they do, is there a reason this is not as good as the more common 2 resistor configuration? I am making the assumption that the coil is an original type 6V coil, but I do not know that for sure. (I guess it was really several questions)
 
" I think I've got it fixed now. "

Well, maybe not.

Which resistor did you remove, the OEM ballast resistor or the fixed resistor?
IMG_20140929_102542_438_zpsc6a740eb.jpg

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" I have a 9N (therefore front mount)12V that does not have the original ballast resistor. My question is couldn't you replace both resistors with one resistor if it is the correct resistor? "

No

Take a look at the picture. Comparing those 2 resistors is like comparing apples to oranges. Well, maybe oranges to tangerines.

Both are resistors. But, the OEM ballast resistor has a value of .03 ohms cold & 1.7 hot. Think of it as a variable resistor. The fixed resistor is just that: it has a fixed value no matter what the temp is.

The concept is that the tractor needs more current for a cold start. After the engine warms up, the ballast resistor heats up & reduces coil current to about 3.5 amps.

Bottom line.....yes, you can add one resistor of a higher value......but you will sacrifice the higher current at start up. I'm sure your tractor starts fine, but as it gets some wear & the temps drop, you'll be happier to have more coil current at start up.
IMG_20140929_102542_438_zpsc6a740eb.jpg

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Maybe I finally asked the question the right way, but this is the first time it was explained so I really understand it. So, if I were to replace the resistor with 2 proper ones, does the order of the resistors matter? Also I am still trying to wrap my head around someone who supposedly knew what they were doing only having the one resistor. Using the values in your example, could there be a ballast resistor that has 1.13ohm resistance cold and 2.8 ohm resistance hot? I am just trying to convince myself that he really did know what he was doing!
 
(quoted from post at 10:46:13 08/29/15) Maybe I finally asked the question the right way, but this is the first time it was explained so I really understand it. So, if I were to replace the resistor with 2 proper ones, does the order of the resistors matter? Also I am still trying to wrap my head around someone who supposedly knew what they were doing only having the one resistor. Using the values in your example, could there be a ballast resistor that has 1.13ohm resistance cold and 2.8 ohm resistance hot? I am just trying to convince myself that he really did know what he was doing!

Do do it correctly, you need to measure the resistance of the coil. Then use 1 ohm as the value of the OEM ballast resistor. On a 12 volt system you need at least 2.5 ohms in the coil. 3 is better. At a total of 3.5 ohms your running current is at the max of 4.1 amps. If you are using a 6 volt coil divide 7.4 volts by the sum of coil resistance and 1 ohm for the ballast resistor. Then add enough resistance to get the coil current to 3.5 amps

So, measure your coil and resistors and post back with your running current. My bet is that it's 4 amps or less. And that will be your starting current as well.
 
It doesn't seem right, but I repeatedly got 1 ohm for the resistor and 0.9 ohm for the coil. (You measure the coil resistance between the connection at the top and the spring on the bottom, right?) It's a small multimeter I purchased an electrical supply shop, not Harbor Freight so I think it's working correctly. I get 0.1 ohm when the probes are touched together.
 
(quoted from post at 13:17:46 08/29/15) It doesn't seem right, but I repeatedly got 1 ohm for the resistor and 0.9 ohm for the coil. (You measure the coil resistance between the connection at the top and the spring on the bottom, right?) It's a small multimeter I purchased an electrical supply shop, not Harbor Freight so I think it's working correctly. I get 0.1 ohm when the probes are touched together.

12 volt conversion right? Do you have one or two resistors in the circuit? Sounds like a 6v coil. If you only have one resistor you've got 1.08 ohms resistance in the circuit. At 14.5 volts and 1.08 ohms, that's waaaaay too much current. Meaning the coil will melt. Because that hasn't happened, you have a meter or measuring issue. Or more than resistor.
 
(quoted from post at 14:50:11 08/29/15) 1.8 rather than 1.08, but still way too little. I'll get a hold of a different meter.

Agreed. That's 8 amps. Just one fixed resistor? No OEM ballast resistor?
 
Yes, just 1 resistor. That's why I was asking if someone could make a resistor that could the job of both. This one doesn't, because the resistance is the same hot or cold, but I'm still using the same meter. The tractor works fine now and has for quite a while so I'm not in a hurry to do anything, but I do want to make it right. The first issue is the lack of resistance in the coil. I assume the coil would not work if the number is correct, so my first job will be to get a hold of another meter. I'll get in touch then, but it will be a few days.
 
(quoted from post at 13:55:27 08/30/15) Yes, just 1 resistor. That's why I was asking if someone could make a resistor that could the job of both. This one doesn't, because the resistance is the same hot or cold, but I'm still using the same meter. The tractor works fine now and has for quite a while so I'm not in a hurry to do anything, but I do want to make it right. The first issue is the lack of resistance in the coil. I assume the coil would not work if the number is correct, so my first job will be to get a hold of another meter. I'll get in touch then, but it will be a few days.

OK. But try & check the resistor when it's hot. It's possible....as in winning the lottery possible.....that it is really a ballast resistor. IIRC, old Plymouths had them on the firewall.
 
(quoted from post at 09:37:34 08/29/15) " I think I've got it fixed now. "

Well, maybe not.

Which resistor did you remove, the OEM ballast resistor or the fixed resistor?
IMG_20140929_102542_438_zpsc6a740eb.jpg

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OK, I removed a fixed resistor. There is an OEM Ballast Resistor under the "hood" but it wasn't connected to anything so I'm going to assume that it isn't working. I'm finding that my tractor is pretty jacked up. I'll get a OEM Ballast Resistor and get it installed correctly and see if that takes care of my problems. I'm getting a better understanding of this each time I log in. So, in summary, with a 12v system, I need the OEM resistor installed correctly, NO additional fixed resistors, and a 12v coil. Now do I have it?
 

I found this part here on Yesterday's Tractors, this is the OEM Ballast Resistor we are talking about?

http://www.yesterdaystractors.com/Ford-8N_Resistor-Assembly_A8NN12250A.html
 
Yes, this is the OEM ballast resistor attached to the terminal block:

http://www.yesterdaystractors.com/Ford-8N_Resistor-Assembly_A8NN12250A.html

" So, in summary, with a 12v system, I need the OEM resistor installed correctly, NO additional fixed resistors, and a 12v coil."

That is correct (tip # 30)

" Now do I have it?"

If you have a 12 volt coil. Do you? Measure the resistance in the coil; if it's 2.5 ohms or more, it's a 12v coil. Or measure the current.
measuring_coil_current.jpg

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