I thought the issue was that the criteria the FAA mandates for separation of critical wire bundles had been updated since the 767 was first certified in the early 80s but Boeing didn't comply with the updated rules for the 767-2C which has many more miles of wiring than a standard 767.
Originally Posted by
KenV
Wire harnesses were designed using civil requirements, but USAF insisted (properly) they should have been done to military requirements. That cost about one third of the delay.