what size ballast resistor

The ballast resistor on my Ford 800 broke and I am wondering if anyone knows what resistance I need. The tractor is wired for 12 volts and the coil has between 1 and 2 ohms resistance.
Thanks

(quoted from post at 12:24:29 10/13/17) The ballast resistor on my Ford 800 broke and I am wondering if anyone knows what resistance I need. The tractor is wired for 12 volts and the coil has between 1 and 2 ohms resistance.
Thanks

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ou need a resistor that will yield 4 amperes coil current (SS points closed). In vicinity of 1.6 Ohms.

I think all ballast resistors would be the same resistance, 1.5 ohms. Think about Ohms law, to reduce the voltage through your coil from 12V to 6V, the ballast resistor needs to match the resistance of the coil.

mid 60s chevy biscayne 6 cylinder resistor is fine. Jim

If you have a local O'Reilly's auto part store just ask for a VR-1 or VR-2

Chrysler, Ford, and G.M. all used different proprietary coils and the appropriate corresponding resistors. Resistors and coils are different!

(quoted from post at 13:28:52 10/13/17) Chrysler, Ford, and G.M. all used different proprietary coils and the appropriate corresponding resistors. Resistors and coils are different!

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es and ballast resistors are different, ranging from around 0.3 to over 2 Ohms. Which is exactly why I said, select for 4 amperes SS current. I didn't mention voltage, you will notice!

(quoted from post at 11:04:21 10/13/17)

(quoted from post at 13:28:52 10/13/17) Chrysler, Ford, and G.M. all used different proprietary coils and the appropriate corresponding resistors. Resistors and coils are different!

Click to expand...

es and ballast resistors are different, ranging from around 0.3 to over 2 Ohms. Which is exactly why I said, select for 4 amperes SS current. I didn't mention voltage, you will notice!

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quote]Thanks for the advice. Life would be easier if the resistance was actually marked on the resistor.[/quote]

(quoted from post at 14:53:41 10/13/17)

(quoted from post at 11:04:21 10/13/17)

(quoted from post at 13:28:52 10/13/17) Chrysler, Ford, and G.M. all used different proprietary coils and the appropriate corresponding resistors. Resistors and coils are different!

Click to expand...

es and ballast resistors are different, ranging from around 0.3 to over 2 Ohms. Which is exactly why I said, select for 4 amperes SS current. I didn't mention voltage, you will notice!

Click to expand...

quote]Thanks for the advice. Life would be easier if the resistance was actually marked on the resistor.

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/quote]Maybe, but most auto supply stores can't even tell you the resistance of what they sell & to top it off, one common 8NE10306 resistor has been found to have values differing by as much as 3 to one!!!! "Quality" as we once knew it is gone!

Plus a cheap multimeter is more likely to accurately measure 4 amps VS measuring a 1.5 ohm difference between a 6V VS 12V coil primary.

You say the coil has a resistance between 1 and 2 ohms (sounds like its a 6 volt coil)

IF THAT MEANS ITS 1.5 OHMS ????? in order to achieve a 50 50 voltage divider so the ballast drops 6 volts leaving 6 volts for a 6 volt coil,,,,,,,,,, THE BALLAST NEEDS TO BE THE SAME RESISTANCE AS THE COIL

Many typical old farm tractor 6 volt coils have around 1.2 to under 2 ohms (1.5 typical) LV Primary resistance, so if used on a 12 volt tractor the ballast would also be 1.2 to under 2 ohms.

In the alternative, its not good to switch over 4 amps of current using mechanical ignition points, and since I = E/R, use 4 = 12/R which means the TOTAL of coil PLUS ballast resistance needs to be at least 3 ohms..........IE If the coil is 1.5 then the ballast needs to be 1.5 as 1.5 + 1.5 = 3 ohms and that combination would draw 4 amps.

NOTE under charge the battery voltage may rise to 13+ or so !!!!!!!!!! The figures above are an illustration ONLY

Got it ?? post back any questions

John T

Ditch the ballast resistor all together.
Replace the coil with a true 12V coil. NAPA IC14SB or equivalent.
About $15 locally. Less connections to corrode. Less headache.