It's the frame wiring harness, and no, you can't get it at a parts store. But you don't need one - just repair whatever is wrong with yours. Unless the truck caught fire, it's quicker, cheaper, & better to repair what you have than to try to replace it. You can buy most (if not ALL) of the connectors from Ford or a parts store, and primary wire in various colors, and split-loom sheathing, and electrical tape and crimp connectors and solder and heat-shrink tubing...
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If you decide you have to have a complete new replacement, the only guy I'd trust to make one is Ryan at http://rjminjectiontech.com/ . He's familiar with older Ford trucks and produces wiring harnesses commercially, so he knows what he's doing.
If you want a used one and can't find it locally, I can probably get you one. But you'll have to specify ALL of your truck's options: year, wheelbase, number of gas tanks, trailer package, engine size, transmission model... Read this post & then e-mail me.