key on not running draw

Also still strange that the ammeter didn't move while the battery voltage dropped. Its always possible the ammeter movement is damaged, but again worth figuring out. Flip the headlights on with the engine off. You can do it with key off so green wire issue out of the picture. The ammeter should move noticibley toward discharge. About 9 amps give or take depending on what headlights are installed. The battery voltage should drop a little. Measure how much.
That will (a) provide a comaprison for the voltage drop seen when the green wire is connected with key in run.
(b) prove whetehr the ammeter is working (whether its at fault or been rewired can deal with afterword).