I would think you'd put new on there anyway, instead of using old. Which ones are you refering to specifically whe you say "old"?
Is this the new harnes that Eric was working on? If so, I think the reason they didn't set it up for the "stock" Bronco and let those modifiers out there worry about changing things, was that, through the feedback they got here, practically everyone they talked to had changed one thing or another. Making the stock configuration in the minority. Not only that, but it was made to accommodate every year Bronco and even Ford changed the routing over the years, so stock is still multiple configurations. Painless didn't want to make separate harnesses or have them work for only a few model years.
Back to yours, you can get new headlight plugs, new temp/press sender plugs, alternator and regulator plugs, new ignition coil and even Duraspark plugs, at the local auto parts stores. Weather-Paks complete the rest. About the only thing you aren't likely to find without a trip to the boneyard are the stock horn relay 3-prong connector (later models only) and the windshield washer pump plug.
Are those the kinds of things you were talking about? Or something else?
Paul