Life is full of mysteries...
Opened the AQ-1 connector and [again] ohm-metered the four USB wires to the laptop plug; all was good, nothing intermittent while "jiggling" all of harness. Put it back together, powered it up, checked 5v and switched 12v, and- laptop now shows "AQ-1" connected"!
But then it showed "firmware update required". With my son to guide me (he's head of IT for a local school), we stepped through the firmware update. It's now showing live display of at least some inputs- the two position sensors I added (hurray!) and the four EGTs. I need to figure a way to confirm air/fuel ratio and RPM and boost pressure inputs without the engine running.
So progress is being made, albeit slowly.