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I looked at my used harnesses, but they are all pretty frayed, so no help. Those 1969 GT-350/GT-500 have the same part number as 1969 Cougar XR7, C9WY-14405-B.
The Cougar taillight harness is not a direct replacement as you seem to imply in your post. It is not the same harness. The Shelby tail light harness for one uses a separate clip that grounds each separate receptacle in the Shelby fiberglass taillight panel. Cougars don't need that because the Cougar tailpanel is metal. Consequently you have to modify a Cougar taillight harness so that it will function in a Shelby.