We have discussed in the past about the special ECU based ground the connects to the transmission., my LM based car has this. If this line is not connected the car won't start. I would guess this is for a neutral safety switch that my MTX does not have.
I don't see this ground at the transmission area for my new SBEC based harness but ECU does send a line into the cabin that is currently terminated to ground with a jumped connector which I have seen in a 92 manual listed as a clutch switch.
I have studied the SBEC ECU connections but I don't see anything that requires a transmission ground for the ECU. I just want to be sure before I attempt to start the car.