Really Jammed up Bad! 25K paperweight Cummins ISX Replacement

Do you have access to the donor ecm harness?

 

Yes

 

At the ecm, peel back the protective loom cover and take a few pictures of the wire layout.
Do the same at the receiver truck's loom.

Also "supermiller" . com has lots of wiring diagrams. Check them out too.

If when you turn the key on, the system goes through self diagnostics properly, but the dash just isn't lighting up, it's likely a simple pin swap. Truck options difference may dictate this inconsistency.