Over in 7.3 we got a guy that wants to tow, but is missing an electrical part from his towing package.
It consists of a harness that has a small "doghouse" with two relays inside, and two cables coming out, one male, one female. A chassis harness connector is de-mated and these two connectors are inserted in-line to provide relay isolation for trailer battery charging, and trailer back-up lamps.
I believe this is all he needs, as he should already have the rear 7-pin connector. I don't know how he got all the other stuff without this harness, but that's how it appears, because he only has one doghouse beside his under-hood fuse/relay block.
Any parts numbers on this, and is it still available? Gotta' bet it's pricey this far down the road, though I found one on eBay about four years ago pretty reasonable. Wish I'd have saved the part numbers.