Most coils that need a resistor function best with around 9 to 9.5 volts applied to them, so if your voltage at the battery posts is 12.5V or so, you should be able to put both voltmeter leads across the resistor and see about a 3V drop with the points closed. If the points have some resistance instead of providing a "zero volts" drop when they close, the voltage the resistor drops will be less. The sum of all the voltage losses in the circuit will always equal battery voltage, so let's say the resistor drops 3V, and the coil primary drops 8.9V., then the voltage upstream of the points will be 0.6V with a battery terminal voltage of 12.5. That indicates the points are a little dirty, as the drop across the points should be virtually zero. With clean points, the resistor will consume a bit more voltage, assuming the current flow through the coil windings stays the same.
Try pulling the coil wire out of the distributor cap and holding it about 1/2" from a ground such as the cylinder head as someone spins the starter. You should get a spark every time the points close, then open. The "old mechanics' tale" about a "hot blue spark" went out of style about 50 years ago when resistance plug wires came along- - - -a normal spark will be sort of a yellow-orange color unless you happen to be running solid wire conductors. As long as the spark will jump 3/8" or more, you've got plenty of voltage to fire a plug efficiently. If you're getting a good spark at the coil wire, but little or no spark at the plugs, check the distributor cap and/or rotor for problems.
Jerry
