Ignition systems OEM or?

Points or Chrysler ECU:
Coil start up is at battery voltage. If the voltage during start is less than 9.5 Volts, starting will be more difficult. Voltage at the battery drops during start up, so if you measure before and after its not that informative.

Coil while running will be system voltage reduced by some amount. That amount will depend on the the current draw of the coil, the resistor, and the resistor temperature. 8 to 11 Volts is a range I'd expect. To measure accurately at the coil use a scope.

Chrysler ECU during startup will see slightly less voltage than battery voltage. How much less depends on whether it uses an auxillery resistor.

ECU 4 pin, running sees system voltage on the power feed in.
ECU 5 pin, as above plus running voltage on the fifth pin is reduced by the auxillery resistor.