Just so you know. the coil body does not require grounding.
I would run a 12v wire direct from the battery+ to the coil+ and module+ and try it that way.
This eliminates all the old ballast wire questions and gives a known good supply with nothing to cause drops.
Also when swapping to HEI I tie all the ballast wires together at one point.
Usually ign1, ign2 and the regulator (sense) wire blue, and the new coil+ wire.