Some quick back story, I’m swapping a ‘93 DE-T into my S10. I currently have an auto trans mounted and mocked up in the truck. My basic question and problem is that the layout of the Nissan harness’s confuse me. 1) I have the ATC, but none of the plugs on the trans plug into the atc. So I’m confused what the trans harness plugs into and what plugs into the ATC. 2) I have my engine harness plugged into the motor, but there’s no plugs for the alt, compressor, or the starter. Are these plugs on a different harness that I don’t have?

Changing directions and going stick isn’t out of the question, but I have the auto mocked up and some pieces for it already. I feel like electronically, I may be better off with the stick though.

Depends on what your goals are for the truck. Interesting swap. I'm largely ignorant of what the power limits are on the autos; most people swap to manual transmission. I haven't ever heard of anyone extolling the virtues of the Nissan auto transmissions in S-chassis cars. I know they're heavy AF compared to the manual counterparts and for the S-chassis cars at least, kind of kill the spirit of driving a sports car IMHO. I know the manual couldn't hack it on my KA-T build and I ended up swapping to a Z32 manual transmission around 400whp/wtq FWIW.

https://www.nicoclub.com/nissan-service-manuals

You're in luck. This site hosts the factory service manuals for most nissans. I'd download anything from 1991-1994 for the 240sx and it'll have the pinouts and routing for the harnesses and an AT chapter to cover the slush box. Beyond that, I'm, not a ton of help on that transmission. Hopefully someone more experienced will chime in.

As far as question 2 goes, yes, there is a SUB harness for all of those accessories. You can get one from wiring specialties or make one of your own, it's not hugely complex.

https://www.wiringspecialties.com/s13katrha.html

Unfortunately theirs is for the manual transmission. You could modify it or try to locate one for an auto trans maybe from a junk yard? didn't really find much in a cursory check on ebay.

Nuke, my goal is a very conservative 250-300hp. It’s a show truck, it’s on air ride, and I’m not trying to break any records, just do a motor swap in an S10 that’s not a SBC.

Like I said, I’m not “married” to the auto trans, but sometimes it’s just easier to put a car in D and cruise. That being said, the manual trans might just be the easier swap time wise and mental health wise.