[supereal]

The wave form shows a TMS (root mean square) reading when the engine is running. The correct resistor is wound with nichrome wire that changes resistance as the voltage increases in the system to prevent damage to the ignition points and coil. The ohm value of the resistor out of the circuit would be in the range you say. The voltage in the vehicle system varies as the generator speed follows the engine speed. The resistor is a somewhat crude, but effective, "voltage regulator" for the ignition system.