I'm trying to figure out where this connector is supposed to be plugged into (if at all, I'm guessing its for the SC400?)

This is in the dash, up above the ECU

 

im going to make a guess and say that's probably the connector that supposed to hook up to the in-car phone option for back in the day. If it's taped up like that on the wiring harness and not hooked up to anything it means that its set aside for optional components.

 

Maybe it is the car phone. I have no idea to be honest.

I should probably take a look inside of my SC sometime.

 

Well if anyone gets bored and wants to look under there and their kick guard is already off be my guest!

As far as the phone thing goes, that would make sense.