new alternator...shows decreasing voltage after you get it started (usualy by pop starting) and runs till battery voltage gets too low for ECM, is there a possible fuse somewhere?? Car will jump start after extended connection, and continue to just run battery down. Semi rats nest of wires going between alternator and battery. Even when battery shows good voltage, same mojo, decreasing while engine is running, battery was charged and tested good by advance auto. I am borderline at my wits end because of non factory wiring. I can take pics if it will help diagnose this, thanks. Car is an 87 Vette.