I keep seeing wiring harnesses up for sale that are listed as 70 through 72 A body compatible.
I know most people think they are but it’s not the case.
The GM harnesses were changed between 71 and 72 and the 72 will not work for the 70 and 71, nor will the 70/71 work for the 72.
I know this to be true, as I found it out the hard way and it was confirmed buy an exhausting search of the GM archives.
Someone told me that the connection tabs at the firewall could be changed around to make them work either way. Ok I said I’d try that, WRONG believe me it's not wroth it. I am not trying to be a smart, this is just FYI for you.
Paul

Not only difference from year to year but model to model, SS or not, gage or idiot lights.

Yes all that also.
I just wish the posters on eBay knew all this stuff as well. I have gone so far as to email some of them with this info and most just tell me to get bent or worse.
A lot of them have started putting in a disclaimer so they don't have to do any research on their own.

That's Ebay!
You need to know what you need, don't go by what anyone on there writes, you'll get burned most the time.

Pat