There are different, separate harnesses for different parts / areas of the car.
I assume you are talking about replacing the harness in the engine compartment?
Most especially the harness which is under the intake manifold, and which goes under the front of the block?
This harness wears out first, and failure is endemic.
I replaced mine.
I sourced the replacement in a U Pull It yard; the prior owner seemed to have replaced his recently, it seemed nearly new (nice find).
I removed the intake manifold, and with that off, it was pretty simple.
Just an exercise in logic, really.