Help me name this part, please?

Is that mounted on the fuel tank bracket?

 

Is that yellow plug on the backside in the picture connected to it?

 

In the first pic, upper right corner, between the white threads and orange threads is a quick release valve (QR) which threads into the tractor protection valve (TP). The valve below that I think is called the double check valve. The wires are for the trailer brake light switch.

 

As long as your hands are dirty, you might as well change the rest of the connectors around there, and save yourself some time.

Get the brass one's.