Wiring harness advice

For the engine harness, buy new. They are reasonably priced and originals are almost always trashed.
For the dash harness you can usually find good original ones. Rear harness usually hold up well but may need some work in the trunk area. These are not too expensive so it may be easier just to buy new.
The dash harness is very expensive and they are usually fine other than maybe some hacked stereo wires.