I agree with David, and believe the injector wiring goes straight from the ECU to the injector plugs.

IMO, you haven't yet verified The Fuel relay operation beyond that first "click when the Key goes to position II — which does nothing directly to the pumps in terms of the normal Fuel relay control needed for starting and running

At key position II, the System relay conditions the ECU, AMM, and Fuel relay to become active when the engine is cranked — and then the ECU activates the Fuel relay, but only after getting "Ignition OK" pulses from the Ignition CU.

You said you "believed" you heard the pumps when you jumpered fuses 4 and 6. I wish you or a helper had reached under the car to be sure. I should have suggested that you try starting while the fuses were jumpered too. That might have told us something more.

I have to question the "shop" that thinks the grey plug has any wires that could cause a no-start with your symptoms. Or any no-start, unless it has more wires than David or I know about.

Hope it's really fixed, but...