39 ford coil....ballast resistor required?

[37coop]

Hi guys as in the title...my 39 coupe runs good ,it's not got the original distributor but a later I think they call it a crab type with a separate coil I was told it would need to be using a ballast resistor with the coil,it's been converted to 12volt.electrics is a whole new science to me so any advice would be grateful, thanks. Jim.

[Kurt in NJ]

It depends on what coil was used, you will need to measure the primary winding resistance, or find markings on the coil

[rotorwrench]

12-volt will need a ballast if it has the lower resistance primary winding. Many of the newer manufacture coils print the need for ballast on the body of the can. A person has to be aware that coils for electronic ignitions are available that have a lot higher resistance in the primary than a point type ignition can take. I actually prefer one of the coils used in the 12-volt systems of the mid 50s to the mid 60s with a 1.3 to 1.5 Ohm ballast. That keeps the heat out of the coil and in the ballast where it should be.

[37coop]

Yup I reckon I,ll fit one,I have bought a 12 v coil and ballast as a pair with a message on the coil stating its for a ballast but the coil presently on it is a pertonix flame thrower so I guess a swop is the answer ....many thanks

[AnthonyG]

Just a heads up, make sure your not running through two ballast r's. You will more than likely have one in your starter /ignition circuit under your dash. ( not sure on '39, my '35 was that way ). Typically the new one for your electronic dist. / coil you'll locate near the coil under the hood. I overlooked the under dash stock one when I converted to electronic dist. and had both in the circuit inadvertently creating too much resistance and engine would breakup over 1200 to 1500 rpm. Took a while figure out my dumb move.

[37coop]

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Originally Posted by AnthonyG

Just a heads up, make sure your not running through two ballast r's. You will more than likely have one in your starter /ignition circuit under your dash. ( not sure on '39, my '35 was that way ). Typically the new one for your electronic dist. / coil you'll locate near the coil under the hood. I overlooked the under dash stock one when I converted to electronic dist. and had both in the circuit inadvertently creating too much resistance and engine would breakup over 1200 to 1500 rpm. Took a while figure out my dumb move.

ThanksAnthony, I, will have an investigation on that one.

[JSeery]

What you are looking for is a total resistance of around 3.0 ohms, so with a 1.5 ohm coil you want a 1.5 ohm ballast resistor. The flamethrower most likely had way to low resistance and had a fairly short life!