IMO most likely at or towards the dashboard (right) fuse block assembly since that has been a known issue for some Regal and Grand Prix "W" body car owners. I recall corrosion issues or wiring directly at the fuse block.
Note: Until that is fixed I believe you will be missing 12 volts to the ALDL odb-ii port so a typical odb-ii scanner will not work if it needs to power off the port.