AC Wiring harness vs. Non-AC Wiring harness

Jim Kueneman said

You will have to look inside to figure out which position the blue and green wire are in the firewall connector. That changes from year to year.

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Makes sense. I figure I will need to double check a few things when plugin it up just to make sure things are correctly located....
On a similar yet separate note, have you any experience with using aftermarket gauges? Since I am moving away from the OEM cluster, I will need to retro the multi-pin connector that plugs into the factory circuit board. Was just wondering how that fairs.....