Snap and Complete Power Shut Down
 

Turn the key to the initial power position and everything powers up as normal.
Turn the key to the start position and there is a snap sound and all power goes off.
Disconnect the battery and the system resets, ready to repeat.
This happens when the engine wiring harness is fully connected and when everything is disconnected less the starter.
Starter is wired correctly based on all the pictures that I have seen.

Any idea what could be causing this?

UPDATE: Disconnected the red wire from the starter. All grounds are good. The snap sound is the starter solenoid. Now the power does not go off.
Do I need a new starter - is abrupt failure like this possible?

UPDATE2: Apparently, while doing other work, the main system relay went bad! Replaced that all is good now.

UPDATE3: All is not so good. Every couple of days, the main system relay trips on startup and the battery has to be dis/reconnected to reset the relay. No OBD2 codes in the system, at least no standard codes. Not sure how to pursue resolution now ...

Good to hear you got it sorted