Check the DC Ohm resistance of a pickup to make sure the wound coil is working properly and it’s in the proper range.
Visual inspection of the pickup to see if it’s been rewound or wound in the proper direction.
Make sure if the pickups been rewound, it is professionally done with the proper gauge of magnet wire, wound in the right direcon and check the magnetism for proper gauss and polarity.
Inspect the pickup to see if it’s been hooked up and the wires are properly connected.
Check for short circuits or broken connections in the lead wire.
Check the magnet polarity and gauss of individual pole magnets or bar magnet.
Check to see the ferrous polepieces conduct the magnetism to the strings.
Check to see that all the proper components in a pickup are there and working properly to create the proper magnetic field through the coils and to the strings.