I still pose the question to you I asked you on 9-8.....i

Is there a "mini DIN" connector (like the one in the plastic bag in your photos) attached to the ECU? It should exit the ECU in the same place as the other wiring does.

That connector is where the mini DIN male connector on the start box attaches for startup. (The gray colored round cable) The engine will not start without that connector installed in the ECU.

Do you have a manual for the engine?

Andy Lo of Electrodynamics made your ECU and might install the plug for you.