What's the plug for that plugs into the Alternator

[DeadsEvolution1]

Ok so this is a total newbie question but I can not find a forum about it on a 1G. I found for a couple 2G's though which doesn't help. Just want to know what the plug is for that plugs into the alternator? I know the other 2 wires the go to the bolt is what sends the voltage back to the battery etc but what is the plug for?

Reason I ask is that my car decided to start sputtering like crazy and than it died. I tried to crank it over and my battery was dead. So i got a jump and let it sit to charge the batter back up, went to roll my windows down and the car bogged down and died again. So immediately I knew it was something to do with the alternator. But I did notice when removing the alternator to get it replaced the wires had electrical tape on them and when I removed the tape it was only help on by a strand or 2 wires. I rewired them correctly with some new wire and soldered it but just want to know problems that would've caused...

 

[97gst_spyder]

The plug is for the ecu to control the voltage that the alternator puts out. The problem could be the voltage regulator.

 

[DeadsEvolution1]

It actually was the alternator that failed. I put a new one is and bam the car is good again just wanted to know what that did since the wires to that plug were so bad