I recently took on my first swap. Replacing a d16y8 in my 99si. (Canadian car). And have ran into a problem. While hooking up the harness to the new motor I broke one of the sensors off of the motor directly under the intake. A round 2 prong plug which threads in and out. Not sure what it's for and not sure if I need It or not! (Picture from old motor also broke pulling motor) THANKS IN ADVANCE!

 

Knock sensor.. U can get another one and replace it. They tend to break easy during swap.
pic for reference.
https://www.google.com/search?q=d16y8+knock+sensor+location&prmd=sivn&sou rce=lnms&tbm=isch&sa=X&ved=0ahUKEwiZqoya0Y7SAhUj24 MKHR5qDp4Q_AUICCgC&biw=1280&bih=800#imgrc=NQ10dAtC 30OUeM:

Look like you got the block heater plug installed also, nice...