Wireing Harness,interchangeabilaty?

[old Chevy guy]

Hey all ! Iv'e started to try and sell some of the extra parts I've acumulated over the past years to A. thin the herd so to speak and B. raise some cash for other projects. I have several cabs to part and was wondering if the wireing was year specific and if so what if any year harnesses would interchange. Right now I'm mostly concerned with underdash but I will take a lessen on whatever I can learn from those who have ventured there before. For instance is a harness with gauges different from one with lights? Thanks