Source : Free On-Line Dictionary of Computing

blue wire
     
        (IBM) Patch wires added to circuit boards at the factory to
        correct design or fabrication problems.  These may be
        necessary if there hasn't been time to design and qualify
        another board version.
     
        Compare {purple wire}, {red wire}, {yellow wire}.
     
        [{Jargon File}]
     
        (1994-11-29)