Alright, so I just bought a 90 Hatch and I'm having trouble identifying where these connections go. They're both male ends. From the diagrams I've read, I believe the larger of the two is part of the main harness. The under the driver's side, left hand drive, Ka24e. (Side note, my tach and spedo don't work- could this be part of the issue? Haven't checked to see if the sensors are hooked up).

the one with the rubber around it is your obd connection, if its a 90 with a 90 wiring harness youll want to order the nissan-1 addapter from snap on, the other one however is a mystery lol

Time to pull the schematic. Should be in the FSM at nissanservicemanual.com.

Congrats on the purchase, and welcome aboard!