Victor,

I am down to my last three workable RX8 coils and
one of those might be dead.

Here is the schematic on the GM coils.
Why do you think they ran a separate signal ground.


Paul Lamar

The high current through the coil can cause ground loops. These loops
could upset the biasing of the trigger circuit or conducting be
conducted back to the computer if using a common ground.  The separate
ground is to make sure that "on" and  "off"  are well controlled without
respect to the quality of the coil ground. The GM coils appear to have a
25K resistor between the signal ground and the power ground.
I use separate supplies for the coil (12 v gel-cel) and trigger circuit
and use a small wire to tie the two supplies together.

Victor

I am using two supplies as well. The shield is grounded on both ends.
One end to coil signal ground and the other to the 5 volt
supply. I am on the way out the door to get a spark plug
Wire and move the spark away from the coil.

Paul Lamar