[Already Gone]

I bought one of your harness for my 1972 C10. I am getting to install and have few questions. In the picture with black plastic plug with a spot to put screw through, what is it and do I just attach it to the truck somewhere. What does the white plug plug into. I'm thinking its to plugmy headlight on warning buzzer wiring into? The other pictures are those pins and I se something written there but don't understand what you mean. I asked about them when I received the harness and you went me the other half of the pins but I have no clue what they are or where they go. The rest of the wires you have labelled and those are pretty straight forward. Thanks in advance.