When cranking, the ballast resistor should be bypassed with the ignition switch on "start". The coil gets full battery voltage which is pulled down by the load of the starter. 8 volts sounds about right or maybe a touch low. Still should be plenty to make a decent spark.

You could check voltage at the battery while cranking... if its 8 volts or a bit more, all is well with the wiring. If you get much difference (more than .75 volts or so) there may be some dirty connections (bulkhead or ignition switch or other).