Burned my resistor

49 8n 12v system, with new 6v coil, points, condenser, plugs, wires and Napa/sparex ballast resistor. Tractor started and ran great, then over a period of a couple days became harder to start until it wouldn?t start. Found no voltage on the downstream side of ballast resistor; looks like some arcing went on and the element is broken. I don?t want to put another new ballast resistor in until I know what caused failure of this one. Any thoughts?
Thanks in advance.

See tip # 30.

Get a 12v coil and the oem ballast resistor.

That's all you need.
75 Tips

where does one find an OEM ballast resistor.?

Locate on the tractor?

It's on the left side of the dash support. On top of the terminal block.

You can buy one here or at nnalert's or Dennis Carpenter.

It's .3 ohms cold and 1.7 ohms hot.
75 Tips

Did you use a WIRING PICTOGRAM BY JMOR for the correct way to do a 12V switch-over job on your early 8N? If you used a 6V coil on a front mount 12V system, you needed to add an inline ceramic 1-OHM resistor as well. By swapping out the 6V coil with a true 12V coil, you do not use the extra resistor in the circuit. You need to verify the entire wiring system is correct using the Pictograms as your guide before applying any power. You can test the resistor by measuring across the two terminals with your VOM. Just because it is harder to start now does not mean you fried the resistor. Discoloration means nothing. Resistors get HOT, and when new, will smoke a bit as they do and burn off the coating residue. Your hard starting issue now could be fuel related. Correct the wiring first then use '75 Tips For N-Owners' by Bruce(VA) to diagnose fuel flow via test procedure. Your problem is either in incorrect wiring or poor fuel flow, or a combination of both.


EARLY 1948 FORD 8N RESTORATION WITH CORRECT WIRING ON DASH PANEL:

Tim *PloughNman* Daley(MI)
OEM BALLAST RESISTOR

Wiring is new and correct per the diagrams you directed me to. I purchased a new ballast resistor from NAPA and installed it with the new wiring. The tractor started and ran great for 2 or 3 days. On day 4 I notice it started hard. On day 5 it started really hard and then no start. Checked for spark, no spark. Checked for voltage at top of front 6v coil, no voltage. Checked for voltage on downstream side of new ballast resistor, no voltage. Check for voltage on upstream side of new ballast resistor, 12v. I removed battery and checked for continuity across new ballast resistor, ballast resistor is open. Upon further inspection the resistor is physically broken and it is evident that there was arcing going on both on and near the ballast resistor.
Ive checked for a short to ground within the ignition circuit but it appears the circuit is good. My thought is I purchased a defective resistor however at $26 bucks each I?d like to make sure before I install another. Is there a way to measure the ?hot? resistance of a new ballast resistor prior to installing it?
Thanks

I don't think you had a defective resistor. For it to self-destruct like that would lead me to believe the wiring wasn't quite right. Verify that again and if you don't use the ceramic 1-OHM inline resistor with a 6V coil, you will pump more current thru things. Also, you don't need to buy and replace an entire assembly. The resistor itself only needs to be purchased for like $6. The resistor is p/n 9N-12250, has screw terminals on each side of the resistor itself, and a single terminal post junction only on the bottom. It is passive, only a junction for three wires to fasten to. The base is screwed onto the dash via two screws. nnalert has the resistor only. With VOM set to OHMS, measure the resistor across both top terminals only static and see what the value is.

TPD

Thanks, I?ve double checked the wiring from the terminal post through key switch through ceramic resistor through ballast resistor to coil, points & ground when points are closed. Unless I have a intermittent short to ground I believe the circuit is correct.
I?m able to check the cold resistance of a new ballast resistor as you stated, is there a way to check the hot resistance prior to installing a new ballast resistor to ensure it is reaching the correct 1.4 ohm operating resistance?

(quoted from post at 11:39:49 10/13/18) Thanks, I?ve double checked the wiring from the terminal post through key switch through ceramic resistor through ballast resistor to coil, points & ground when points are closed. Unless I have a intermittent short to ground I believe the circuit is correct.
I?m able to check the cold resistance of a new ballast resistor as you stated, is there a way to check the hot resistance prior to installing a new ballast resistor to ensure it is reaching the correct 1.4 ohm operating resistance?

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ith a variable voltage power supply, you can connect the resistor and advance voltage until current reaches 4 amperes and simultaneously read resistor voltage and current. Divide the voltage by the current and the result is the resistance value hot. Not much need to do that, however, because in normal running (not stalled), it will only be carrying about 1 ampere, so, it will not be much more that warm. If it is red hot, something is very wrong!

rather than messing with another ceramic ballast resistor, why don't u simply do what bruce suggested - namely, forget about that and just get a 12 volt coil instead?

i've been running my 12 volt 2N without that ceramic resistor for 7 years now, with no harmful effects - and i've still got a SIX volt coil. i'm not advising u to do the same, but i AM advising u to move forward without that resistor.

I have had them just go bad. just replace it or buy a 12 v coil and remove it.

(quoted from post at 17:27:05 10/13/18) I have had them just go bad. just replace it or buy a 12 v coil and remove it.

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Thanks for all the suggestions. Unfortunately my 6V coil is brand new so I hate to throw away $50. If I knew a 12V cool would cure my issue I would buy a new one today.
Ceramic resistor as well as the ballast resistor were both brand new when i replaced the coil. I don’t believe the ceramic resistor is the problem. The new ballast resistor got very hot, melted the plastic between the resistive coils and the coil is actually broken. One thing I noticed is that the head of the screws that serve as the wire termination posts sit very flush with the backing plate of the resistor. Any irregularities in the bracket that the ballast resistor is mounted to could cause a short to ground via the screw head(s). Should there be any kind of insulator between the ballast resistor and the tractor mounting plate?
Thanks again

Thanks for the info.
Since I don’t have a variable power supply I was hoping that I could do something like wiring a new ballast resistor in series with a 12v battery and another load such as a auto light bulb or something to simulate the amp draw and heat up the resistor. Any thoughts?

was writing this couple hours ago but got interrupted

You said you put a new SPAREX ballast resistor $26 at NAPA. I assume that would be the OEM style like <a href="http://www.yesterdaystractors.com/Ford-8N_Resistor-Assembly_A8NN12250A.html">this</a>.
I recently purchased one of those to replace a "fixed" resistor on a 2N I rewired. I "perceived" two "defects" in the ballast resistor assembly.
1) The mounting holes did not line up with the holes in the dash, about 1/8" too far apart. Fixed by slotting the holes.
2) Insufficient clearance between the heads of the screws which make the terminals and the back side of the insulating block. Fixed by cutting a piece of fish paper to fit and punching holes aligned with the mounting holes in it, and installing it between the resistor assembly and the dash.

(quoted from post at 19:22:54 10/13/18) was writing this couple hours ago but got interrupted

You said you put a new SPAREX ballast resistor $26 at NAPA. I assume that would be the OEM style like &lt;a href="http://www.yesterdaystractors.com/Ford-8N_Resistor-Assembly_A8NN12250A.html"&gt;this&lt;/a&gt;.
I recently purchased one of those to replace a "fixed" resistor on a 2N I rewired. I "perceived" two "defects" in the ballast resistor assembly.
1) The mounting holes did not line up with the holes in the dash, about 1/8" too far apart. Fixed by slotting the holes.
2) Insufficient clearance between the heads of the screws which make the terminals and the back side of the insulating block. Fixed by cutting a piece of fish paper to fit and punching holes aligned with the mounting holes in it, and installing it between the resistor assembly and the dash.

Click to expand...

Yes, I think you and I are thinking exactly alike. The picture you posted is exactly what I bought. While I didn’t have issues with screw holes lining up I do believe that there is a very good chance of the screw heads coming in contact with the mounting plate on the tractor creating a short to ground. When I initially looked at the resistor I didn’t notice it, however when I removed the resistor this morning it stood out like a sore thumb. When I compared the NAPA resistor to my original ballast resistor the original resistor backing plate is about 3X thicker and the screw heads are counter sunk much deeper. I think we are on to something. It might be a day or two before I can get to town for another resistor but I’ll post back if it cures the problem.
Thanks

(quoted from post at 14:09:49 10/13/18) Thanks for the info.
Since I don’t have a variable power supply I was hoping that I could do something like wiring a new ballast resistor in series with a 12v battery and another load such as a auto light bulb or something to simulate the amp draw and heat up the resistor. Any thoughts?

Click to expand...

ine if you can select bulb(s) or whatever to yield 4 amperes.

After my 6v. generator quit, I changed to 12v. I used a new 12v. coil with the original OEM ballast resister for a 2n. Used original points. I also had to revise the battery box and the battery hold down. One wire alternator. 3 years of operation, no problems.

There are two styles of the ballast resistor -the early 9N/2N one and the later 8N style. Each one has different mounting screws and holes. You motliely got the wrong one if the holes don't line up.

Tim Daley(MI)

If the wiring is all correct, then it's possible the distributor has a short. Take your VOM set to 'continuity'. One probe on the LH top post of the resistor. Place the other probe to ground. Turn key switch ON but don't crank engine. You should see battery voltage with points open, half the value with points closed. If test passes, move to the coil wire post. Same test. If it has continuity then you are getting power to the distributor. If either fails, wiring is mucked up or distributor is mucked up. You need to verify the distributor is functioning correctly before you mount it via continuity testing. You need your VOM -NOT an idiot test light -those require power and you don't want power ON for this. Set to 'continuity'. With pints open, place one test probe on the lobe side and the other test probe to the base ground. You should have continuity. Close points -same test, now NO continuity. If you do, then touching anywhere to ground will show continuity and thus reveal there is short somewhere. Look at your screw where the coil pigtail contacts. Also could be the copper strip from the condenser is broken or missing. Then if unit passes, mount to tractor then do the test first mentioned. If all pass, then it's time to check for spark.

TPD