There was a good dash removal tutorial on hitmans site (78ta.com). This tutorial had some good pics/info on wiring. I think this was the link,
https://www.78ta.com/old/rdash.php
But, just tried the link now and it appears hitman's site is down ? gone ?
As 78w72 says there is a small metal strap between the gauge cluster housing (upper left housing screw on gauges) and the headlight switch screw. It could be easy to miss that small metal strap. So, make sure that small metal strap / ground is there and it is good. I also ran a separate wire from there directly to the metal core of the dash.
Hoghead's Firebird and Trans Am Parts has some good dash wiring pics too, see
https://firebirdtransamparts.com/tec...ss/harness.htm