Need help getting the correct ignition coil!

[RandyBee1]

I have a 1973 F100, it had electronic ignition that I replaced with a conventional system ( ie, points). I picked up a new coil the other day from NAPA, when I went to put it on it said that I must use a resistor wire with the coil. My engine has no resistor wire. I measured both coils and they both had 1.9 ohms. I'm thinking that 1973 was a transition year when the factory started adding electronic ignition and hence upgrading the coil. I probably need to order a newer coil like a 1974 or 1975.

Any thoughts, ideas???

Thanks

Randy B

ps... And before someone asks... the reason I replaced the electronic ignition is because I yanked the engine out a few weeks ago to rust proof the engine compartment and in so doing lost a tiny screw that holds the stator to the distributor. I had a spare NOS distributor in my garage with points, so I stuck it on

[68F250]

Your truck should already have a resistor wire that is located under the dash. Points or Duraspark, Ford still used a resistor wire.

[RandyBee1]

Thanks Barry, I assumed if there was a resistor wire I'd see it somewhere near the coil and or distributor wires. Never thought it would be up near the dash.

Correct me if I'm wrong but the purpose of the resistor wire is just to knock down the coil some so it does not fry the ignition switch right ????

Randy B

[68F250]

Yes, it serves a couple of purposes. Main one is to cut down on the voltage to the coil. This reduces the current going thru the ignition switch, coil and the points. Did you know that our coils were originally 6 Volt coils adapted for 12 Volt use? Another purpose of the resistor wire is to regulate the voltage. The wire has a positive temperature coefficient meaning its resistance goes up with temperature. When charging voltage goes up, the resistor gets hotter and cuts the voltage to the proper level. Also when your engine is idling for a long time, the resistor gets hotter from the coil being in saturation more and cuts down the voltage. A neat feature is being able to bypass the resistor during starting to apply a full 12 Volts to the coil. The full 12 Volts comes from the starter solenoid.