A most important fact has not been mentioned, unless I missed it.
The coil current grounds through the ECU box. So make sure the mounting bolts/screws make good [ clean ] contact with the box AND the car body.
That is true but at this point whether the box is grounded is not the issue
If the ballast was getting 'full' 12v from the key, both sides of the coil would show 12v as it would not be drawing current, if the box was ungrounded
At this point I don't think anyone is sure he getting much out of the bulkhead connector
