coil resistor
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Junior User
Joined: Feb 2005
Posts: 60
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coil resistor
I have a 78 351M motor however the electrical system is out of a 74 motor. I have an old yellow top coil in it that is going bad and I went out and bought an aftermarket coil at Napa. It said use with an external resistor on the side of it. I have always heard that ford coils are internally resisted so I asked the guy at the store about it (he is usually fairly knowledgable). He told me the coil wire acts as a resistor. Is he correct? Can I use this coil?
Thanks
Thanks
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Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
You'll have to find a manual on the year of your truck to see if Ford still used resistor wire. Early trucks (late 60's) used resistor wire to reduce current to the coil. Different aftermarket ignition systems and coils will state if a ballast or external resistor is needed with their coil and trigger system. get it wrong and things end up short lived, resistance added when not required will reduce spark energy to the plugs. Sorry can't nail it for your year truck.
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Moderator
Joined: Jan 2001
Posts: 57,014
Likes: 2,751
From: Virginia
Your truck should have the resistor wire already in the harness. Since these old trucks get rebuilt every few years, after you get it running you can check the voltage at the coil + with a voltmeter. With the truck running, it should be something less than 12, usually 8-10 volts. If it happens to be 12v, someone may have bypassed or cut it out of the harness. It won't hurt to run it a few minutes like this till you make sure it's correct.
