Emergency trailer connector adapter
 

EDIT: Deleted, because I found what I was looking for at Oh Oh O'Reillyyy's.... auto parts! Yowww!

And their part number is?

I am an idiot..
 

Um, Hopkins 47405 does NOT fit.. It is in fact a 7-way round pin to 4 flat adapter, BUT it is much bigger than the connector on the truck!

I ended up having to circumcise the darn thing today and straight-wiring the 4-flat plug into the harness, using only the left and right turn signals, brake light, and ground wires.

I now HAVE to order the right part and splice it in...