You finally explain what that means. So im testing afm fc and isc tomorrow

Look at the wiring diagram and it may be obvious. ;) Test the Vs signal as I've detailed too. Don't go discounting anything because you don't think they fit the bill.... Your gut feeling has yet to provide any reason for me to have faith in it.

ill try to test it today but i have limited time. the main this that seems to be is this crazy volt drop. i still suspect the ecu because before mentioned, jump a car later that day my temp gauge stopped working. got a new sensor did the same thing. notice that my oil pressure gauge jolts a bit but its not plugged in. both of those things are from the computer. alternator is also controlled by the computer. along with all the information that is sent to it and its outputs. when that car shuts off there is no affect to my radio what so ever. and as its dying to the best of my knowledge my lights arent dimming. so its has to be something in the ecu or its wiring because when the car is off im not getting heart stopping voltage drops. i know everyone says that ecu is a last resort but this is not normal.(btw you never get answer my question about the ecu, which one can i put in my car) but im going to test those things like you said after running the car

and as of this morning cygnus is down

Unless I'm completely wrong, the alternator is not controlled by the ecu. It has an internal voltage regulator in the alternator. Also, the voltage you reported at idle is too low, it should still be 13.5 volts. As engine speed changes the available current will change as well, however the voltage should remain constant if the wiring and alternator are both working properly.

Tested the afm and bench tested all it spec along with the isc. Couldnt do fc because I ran out of time. But I found a lead. Ignition switch black and yellow wire. Its apart of the alternator ecu

Alt is brand new and ecu is connected thru battery. From bat to fl am2 to efi fuse then it splices off before main relay as a black and yellow wire

Omfg. Checking my ecu connectors and heard a click. Turn on all electrical loads when I got home and car didnt die...

Should be and commonly is are two different things. Most of the MKIII's I've worked on (except mine after rebuilding harnesses) have a significant drop when loaded heavily... I'm not saying it's proper or optimal. That's beside the point though, the point was that the ECU won't fail until the voltage drop a LOT further then the spec 13.2v to 15v.

No idea who said anything about the ECU being controlled by the ECU.

well based on the next couple of days will verify if that was the real problem. and if it was that I WAS RIGHT HAHAAH ECU RELATED lol