I am just confirming this wiring question. RB25det into 92 s13, there is a black ground wire on the lower engine harness and I'm judging by the 240sx diagram that it is the alternator ground. can I just bolt it to the back of the alternator in one of the holes that are there, or is there a specific place to ground it?

And... I have a connector with a yellow wire red trace and a yellow wire blue trace, and no where to plug it in. Any ideas?

 

The ground you speak of sounds to be the one for the alternator. As for the other plug you'd need to pick up the wiring schematics somewhere online and look it up.