I am not familiar with a DA plug, although I have made a wiring harness that does the same thing.
Looking at the back of the Delco 10SI alternator, you will see the large threaded post that the heavy (10 ga or thicker) attaches to. The two smaller wires go into the side of the case right at the back of the alternator. The terminal CLOSEST to the Batt. terminal is the switched terminal, labeled #1 or I. The other terminal located farther away from the Batt. terminal is the signal wire, labeled #2 or S. The internal regulator needs a voltage signal at this terminal so it knows how much current is needed to maintain required voltage. That is why you just need a small jumper wire from the batt. terminal to the #2 terminal. It can be hot all the time and will not cause any problems.
The #1 terminal is fed from the ignition switch. Any voltage from 2 to 11 volts is acceptable. I use a light bulb in series for feeding the #1 terminal to drop the voltage, but also as an idiot light--if the light is on, the alternator is not charging.
I do not know WHY the #1 terminal should have reduced voltage applied to it. I have studied the wiring diagrams and can't seem to figure it out. My only theory is that when you shut off the engine, the voltage present in the #1 terminal cannot backfeed with enough voltage to keep the coil engergized and the engine running.
