Beside the above you need to verify the wire terminals themselves are good and not loose or cracked. IF not actually closely inspected,just glace at; they can give you misleading views; otherwords, sometimes it may require a magnifying glass. I am pretty sure the wiring uses F56 [Packard, GM, Delphi] terminals for the 1/4" terminals. It just lately that they changing to a different type terminal that I haven't seen enough of these of to know if they are going to holdup and also how to remove from the terminal housing.
The F56 terminal are good but like anything with age they can fail. Otherwords they can make contact at one moment, the next loose it, and then regain it.