so typically as stumpy said, the screws to the frame grounds the circuit board.

if you look the paths on the circuit board end on screws that are not insulated from the circuit.
those are grounds to the gauge cluster.
the cluster is bolted to the frame, and those are your paths to ground.

IF the "chrome" plastic plating is chipped away, or you painted the dash frame, or if some of the screws are missing, you typically get a bad ground for the circuit board.

you can run a ground directly to the circuit board. just look for one of the screws that dead end a circuit path instead of the insulated ones that don't have any circuit going to it.