My M1028A2 is stock wired to power the military trailers I pull with her, including electric brakes on the 5th wheel communications trailer, but had no provision for powering the brakes on my civilian car-hauler.
Rather than build yet another adapter, we put a proper brake controller under the dash yesterday, wired to a civilian 7-way plug mounted under the rear bumper.
Separate wiring was run for the trailer battery and brakes, the lights were tapped into the appropriate military wires. This was done by removing the pins from the plugs, attaching the old and new wires to a new pin, and reinserting them back in the plug. Fortunately DrJay has all the neat stuff for doing that in his shop, and kindly lets me avail of his shop space and knowledge for my projects!
I forgot to take pictures of the wiring plugs after they were put together.
The plug mounting plate was cut out of a piece of steel. The nutserts were just because we were feeling like making it fancy.

It was bolted to holes drilled under the bumper.
The piece of cable on the floor in pic 3 is the excess of what we ran the wires from front to back with.
Cheers
