Human Factors items
Many years ago on a Boeing we had a C-Check. We were supposed to check the engine fire extinguishing squib triggering circuit with a low power meter. What we found out was that bottle one switch position triggered bottle two and vice versa. Boeing had modified the connector keying, so one could not install them to the wrong position.
Also many hydraulic lines to hydraulic power units have now different sizes in their connecting unions, so you cannot install the lines the wrong way.
Cheers
easaman