with a jumper wire with alligator clips on each end jump from the batt positive post to the upstream side of the ballast & see if that gives you enough voltage. If good then check voltage drops when it's idling from the batt positive post to the starter relay to the firewall bulkhead to the ign switch then out to the bulkhead then to the coil positive terminal for the poor connection that is reducing your voltage. The bulkhead is a common culprit. If the jumper wire does not fix it holler back. EDIT is this a 4 pin ECU/2 terminal "single" ballast system?