7 pin(semi) plug to 7 blade utility trailer

I just did this on my truck I pull my gooseneck with. E-Trailer is in fact a one stop shop for this. We simply installed a 7 flat pin recepticle at the rear crossmember and wired from tail light wires right out of the harness end on the truck. Installed a Hayes time delayed brake controller, mounted and wired into cab, ran one wire from it to the back plug for trailer brakes, job done.
Did not change tractors trailer cord plug or wires, so as to be able to still pull fifth wheel trailer with no effort to change back. You do need the trailer brakes to help stop though as others have said.

 

Unfortunately I didn't find that to be the truth. I went and looked as I could of sworn I seen an adapter before but none to be found. Oh there are 7 round to 7 flat adapters but everyone I found specifically said they are not for separate brake/turn lights like a semi has.
Looks like one will just need to get a receptacle and wire it in yourself, or make a pigtail that converts.