I've triple-checked my bench harness connections, and I still can't connect to the ECM with HPtuners Scanner or with a common obd2 reader. I'm getting power and ground to all the correct pins on the ECM and the obd2 port, and I've run the 2500 and 2501 can-bus wires correctly with a 120-ohm resistor installed between the wires.
I have the "check engine" and "powertrain relay" wires grounding out LED lights, and both lights remain lit the entire time the ignition switch is on. I thought the "check engine" light would go out after several seconds, and the "powertrain relay" would cut off after a minute or two.
One last check I thought of, is to power the bench harness with a 12v battery instead of the wall-wart that I've been trying.
Is there anything else I can check before I go shopping for a replacement e38 ECM?