12V coil

Tracy Brown · Jan 6, 2019

I am putting a 12 volt coil on a 12 volt tractor but the coil has written on it "external resistor required". Why is that?
Thanks

David G · Jan 6, 2019

It is really a 6V coil intended for a vehicle with ballast resistor bypass on startup.

Tracy Brown · Jan 6, 2019

So do I need it or not?

JMOR · Jan 6, 2019

(quoted from post at 14:59:16 01/06/19) I am putting a 12 volt coil on a 12 volt tractor but the coil has written on it "external resistor required". Why is that?
Thanks

ecause without it, the current will be too high, resulting in short life of coil and points.

MN valley man · Jan 6, 2019

Yes, you need it or it will eat up the points as was stated.

Duner Wi · Jan 6, 2019

Yes you need it. You can wire it so you supply full battery voltage while starting.
Chevy among others did this to aid starting especially in cold weather or weak battery.
Look at a wiring diagram for 56 Chevy or 1957 350U International.

M-MAN · Jan 6, 2019

You would be better off taking it back and getting one labled no external resistor required. Course if you have a resistor already it would need to be removed. Ballast resistors are a fire hazard.JMO

old · Jan 6, 2019

That is a coil used on things where you have a ballast resister by pass for starting and then you have the resister in line when running and it is really a 6 volt coil used wit ha resister. Take it back and get a coil that says no external resister needed

fixerupper · Jan 6, 2019

Does the old coil have any markings on it or is it painted over? If no markings, find out if your tractor uses a resister and a 6v coil like yours or if it does not have a resistor and uses a 12v coil. No need to horse around rewiring when all you need to do is get the proper coil. Tell us what kind if tractor you have and maybe we can help you out. As a disclaimer, if the wiring has been butchered and changed over to non factory wiring we might not be able to help you just going by tractor model.

tim s · Jan 6, 2019

I agree with M-man..up date it now,,I just did this to a 3020 gas last week,,it was running like crapp (worse than a normal 3020 gas) after all the normal tune up fuel tank flush/carburetor cleaning..I changed the coil and it actually ran nice...

Geo-TH,In · Jan 6, 2019

Jessie,
Did you once say the current will be 4 amps when you
have the right ballast resistor for the coil?
That seems to work on my Jubilee, 4 amps.

dzc3 · Jan 6, 2019

Adding a ballast resistor is not that expensive, Saelle's can get what you need. John is often on here 315 585 9826

JMOR · Jan 6, 2019

(quoted from post at 17:31:49 01/06/19) Jessie,
Did you once say the current will be 4 amps when you
have the right ballast resistor for the coil?
That seems to work on my Jubilee, 4 amps.

es

Tom in TN · Jan 6, 2019

tracy,

You really need a wiring diagram for your specific tractor. My 1975 Ford 2000 three cylinder gas tractor does not have a discreet resistor in the circuit but it has a coil of resistive wire in the circuit so that the voltage to the coil is reduced in normal running mode. I has a plain wire from the starter lug on the ignition switch that provides full 12 volt voltage to the coil when it is starting, then when the ingnition switch is released back to the "on" lug, the coil gets its voltage through the resistive wire.

You would be well served to find a wiring diagram for your tractor.

Tom in TN

buickanddeere · Jan 6, 2019

(quoted from post at 14:59:16 01/06/19) I am putting a 12 volt coil on a 12 volt tractor but the coil has written on it "external resistor required". Why is that?
Thanks

Does the tractor have bypass starting ? This is why 12V coils and ballasts are used .

Elton Fancher · Jan 6, 2019

I recently changed a 300 6 cyl. Ford power unit from dura spark ignition to points. The guy had bought a new coil, 12v and I never thought about needing a resistor on it. It was hottest fire I have ever saw and ate points in a week. I put another set of points in and added a resistor between coil and distributer, that is when I noticed that it said use with external resistor on coil. I always thought long as it was a 12v coil it would work with no resistor. Apparently not.

John T · Jan 6, 2019

but the coil has written on it "external resistor required". Why is that?

WHY IS THAT because its in reality a 6 volt coil so on a 12 volt tractor if you don't add the external series voltage dropping (12 to 6) ballast resistor the coil overheats and the points burn prematurely.....

On a 12 volt tractor you can EITHER use a full true 12 volt coil (no ballast required) or else a 6 volt coil plus the ballast.

John T

David G · Jan 6, 2019

You got a lot of responses, so in summary it might be the right coil if there is a resistance wire from the ignition switch to the coil.

What tractor is it?

Tracy Brown · Jan 6, 2019

It is a Jubilee converted to 12 volt which does not have bypass cranking. I can't return the coil, it came off another parts tractor. I will either install with resistor or see if I have another coil that does not require resistor.
Thanks to all for the feedback.

12V coil

Tracy Brown

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