67 Barracuda instrument voltage conundrum

Failing limiter or just weak ground. This fuel gauge has a slither of metal on its backside that sits against a unpainted spot in housing. This is the chassis ground for the mechanical limiter in the gauge, gauge to housing, housing to dash, ground jumper from firewall to engine block. Only 4 or so of the screws holding the panel in the dash provide housing ground path. Adding a actual ground wire can help lights and all to work better.
If I was facing pulling the panel again, I would install a solid state regulator and good ground path is necessary for it too.