Look at the relay holder number that the wires got to, if main pcm, this would explain a lot.
The wire on the alternator that you show, goes onto the rear of the alt terminal, and then runs into the car to the charge warning light bulb in the clocks, when the alternator is not turning it is of course not charging and so the terminal on the alternator to which the wire is attached is earth, the ohter side of the bulb in the clockset is live from ignition so the bulb glows to show no charge, once the engine starts the live being supplied through the bulb and down the wire to the alternator excites the field windings in the alternator and starts the charge cycle, once started it is no longer needed, until it is stopped again.
As it starts charging the terminal onto which the wire is attached changes to live, of course at the bulb is now a live either side of it, and as you know two lives don't make a bulb work so it goes out showing it is now charging.
tabetha