8n coil resister

[melohn]

what is the purpose of a resister on the coil, Thanks, Jim

 

[JMOR]

(quoted from post at 12:03:49 06/14/23) what is the purpose of a resister on the coil, Thanks, Jim

esired current in a standard coil is in the 4 to 5 amperes range. If coil winding resistance is too low, the resistor is added to limit/control that current. 13v/3=4.33 A, whereas 13/1.6=8.125A, far too high for points or coil. Add 1.6 Ohm resistor to the coil 1.6 and you now have 3.2 Ohms limiting the current. The N series Ford tractors with front mount distributors was a bit different in that the resistor used on those was temperature dependent, being about 0.3 Ohms cold and about 1.7 Ohms when glowing red hot. This not only limited current, but gave a nice boost during starting where the 300 or 400A starter has the 6v battery drawn down to maybe 4.5 -5V.

 

[melohn]

do coils get weak or do they work or not work? and if the resister is not working properly could that cause a miss in the engine? thanks, Jim

 

[Sean in PA]

(quoted from post at 12:48:42 06/14/23) do coils get weak or do they work or not work? and if the resister is not working properly could that cause a miss in the engine? thanks, Jim

Coils can get weak over time as a result of the insulation on individual windings breaking down, but most only exhibit issues at first when things get hot. You won't notice much in the way of a performance difference until it gets to the point where it shuts off after running for 20 or 30 minutes and it won't start again until things have cooled down. Then it will gradually take less time running (not get as hot) for the symptoms to happen, up until it simply won't start at all.

I don't think that a miss is usually caused by a coil going bad.

 

[melohn]

How about the resister, if that wasn't working properly could that somehow contribute to a miss in the engine?

 

[JMOR]

(quoted from post at 15:09:42 06/14/23) How about the resister, if that wasn't working properly could that somehow contribute to a miss in the engine?

esistors of this type are just a piece of wire , so yes, the wire might burn open or short to another part of same wire.. Very, very unusual to find. If you must prove to your self that it is not a problem, place a jumper across resistor when engine missing & see if miss stops. Even doing that , however, might mean coil has a problem that increased current helped clear. Even when all is good, shorting resistor & resulting higher coil current will yield a hotter spark, possibly making up for problems such as bad distributor insulating parts, condenser, wires, spark plugs, etc.

 

[Tim PloughNman Daley]

Do you mean the OEM 9N-12250 BALLAST RESISTOR? It is used on all Fords with the front mount distributor, on both OEM 6V/POS GRN and when doing a 12V switcheroo. If you
switch to 12V and keep your 6V Coil, you need to add an external, 1-OHM in-line ceramic resistor in the coil circuit. Swap 6V Coil to a 12V verified coil and discard
the extra resistor. Have you ever left your Ignition Key Switch ON when shutting down? You may have fried out the coil and burnt the points if left closed. Coil
may work after but as soon as it gets hot will short out internally and shut down tractor. You can test a square coil sort of with your VOM set to OHMS, Probe 1 on top
terminal, Probe 2 on copper pigtail on bottom. A 6V coil should read about 1.5 OHMS. This is not a 100% foolproof method of testing however. You can buy a new
resistor only for $6 and no need to buy the whole base unit if you wan to test further. The wiring must be correct. Incorrect wiring is 99.98% of all system failures.
I advise to go thru entire wiring system before replacing any more parts. Lighting systems are notorious for being culprits of shorts when done incorrectly.

BALLAST RESISTOR, P/N A8NN12250:

FRONT MOUNT COIL TEST:

FORD 8N WIRING DIAGRAMS:

EXTERNAL IN-LINE 1-OHM RESISTOR, USE WITH 12V IF COIL IS 6V:

Tim Daley (MI)