Measuring cranking back at the ballast can be misleading, because ignition power DURING CRANK comes to the coil + (and should be very close to battery voltage, then BACKFEEDS through the ballast, to the junction of the "run" line, and backfeeds into the box to give the box power. NOTE again, this is only for cranking.
So yeh, "key side" of ballast can be fairly low during cranking. Remember, the key "run" power goes dead during cranking
If you are sure that the crank voltage went low at coil +, you either have a bad terminal in the bulkhead connector, a loose terminal in the ignition switch connector, a bad contact in the switch, or some other intermittent bad connection. DON'T FORGET THE BATTERY FEED INTO THE KEY as well!!!
