Its the exciter wire plug. I think that is a stealership part. you can take it apart and fix it yourself. Take the top part of the plastic plug "cover" off by gently popping it loose from sides. Then using a fine punch, push the clip from the bottom toward the direction of where you popped the cover off, if you do it right, the metal clip inside will come out, then you can resolder it together. I think some guy bought a whole new one for $30 when I was reading up on alts on in gen maintenance.
Just be aware, your alternator needs this connection to turn on the volt reg and engauge your alt, if not, your alternator atleast at an idle if not the whole time will not charge the battery or nothing.