Having reinstalled the drivetrain, I wanted to start the engine to check for any issues. It fired up once, then died after a few seconds and would not start again. I noticed that the fuel pump was not priming when I turned on the ignition, the fuel pressure meter I've installed on the fuel rail also confirmed zero fuel pressure. Additionaly, the starter motor did not turn over, all I got was a blackout of all lighting when I turned the key.
I erased a long list of fault codes, removed the fuel pump relay and jumped the 12V supply, but the fuel pump would not run. I started thinking of possible causes; fuel pump faulty due to car being stationary for a whole year, clogged fuel filter, wiring passing over torque tube damaged on removal or reinstall of torque tube. Oh no... removing all of the drivetrain again?! A new $250 fuel pump assembly?!
A web search for "c5 corvette fuel pump not priming" gave multiple hits on corvetteforum.com, and in one of the threads the ground post on the frame inside the LH rear wheel was mentioned. Guess what - I had only put the eyelet connector and nut in place, but not tightened the nut! -A minute later the V8 roared to life.
Other systems are also using this point as a ground reference. The ground point is named G401 in the service manual and is used as common ground in splice pack SP400, where most of the rear sensors and lamps are connected. The schematic doesn't show why the starter motor didn't turn over, but there is probably an interconnection somewhere.