On my conversion harness, one of the pinouts came out, does it just plug back in?

 

It depends, some use solder, and u might have to resolder the connections. Or if it's fancy it should use pinouts like the original ecu harness. Just look at is and it should be pretty easy to tell how it goes back in. If it's too hard to fix u can usually send it back to the seller and they'll fix it.