1974 F100 Duraspark Wiring Help Needed
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04-21-2012, 12:35 PM
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This is CORRECT.
With the key in RUN, the coil is powered through a 1.4-ohm ballast resistor, which is almost the same resistance as the coil primary winding. Half the voltage drops across the coil, and half drops across the ballast. That's why you see about 6 to 7 volts and is NORMAL. The ballast resistor is a long length of special wire embedded in the dash harness.
With the key in START, the ballast is bypassed and the coil is connected directly to 12 volts by the starter solenoid. However, when the engine cranks and the starter draws a heavy amount of current from the battery, "12 volts" is more like 8 to 10 volts. 8 volts is probably a little on the low side, but that's a starting system statement, not an ignition system statement.
With the key in RUN, the coil is powered through a 1.4-ohm ballast resistor, which is almost the same resistance as the coil primary winding. Half the voltage drops across the coil, and half drops across the ballast. That's why you see about 6 to 7 volts and is NORMAL. The ballast resistor is a long length of special wire embedded in the dash harness.
With the key in START, the ballast is bypassed and the coil is connected directly to 12 volts by the starter solenoid. However, when the engine cranks and the starter draws a heavy amount of current from the battery, "12 volts" is more like 8 to 10 volts. 8 volts is probably a little on the low side, but that's a starting system statement, not an ignition system statement.
So can anyone confirm I should be using a 1.5 ohm coil? It's a Pertronix, and their website says that's correct for a 12 V system. They say I should use a 0.7 Ohm coil for a 6V system.
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