That step was intended to verify voltage at the ECM after you had confirmed that you had it at fuse 42. If you look at the right-side diagram in post 33 you will see that pin 73 gets its power through relay 26, and that relay 26 is actuated by the ECM. That means that the ECM has to be plugged in to verify that it is working. I haven't looked at it but I imagine that the ECM connector is sealed, so probing it from the back is not going to work. You may be able to take the backshell off of the connector to get to the pins, or you could use a piercing probe to stab through the wire.JOHNWR, please comment on step 13 re: X1-73
Here are the pinouts of the connectors. It looks like the ones you want are both in X1........So feeling adventurous I pulled the underhood fuse box apart (separated the pieces except for the last layer) didn't see any burn marks or other signs of failure. Near impossible to do a wire trace I don't have a pinout for the fuse box connectors.
Guess the next step is to try the relay swap as suggested.