Dash Wiring Issues

As for dash lights the basic path is headlight switch for power from the rheostat, ( might go to a fuse in the fuse block) then to the connector on the back of the cluster to the cir board to the bulb to the ground via a screw that holds the cluster to the dash frame.

The rheostat could be failing
The pins on the cir board could be failing
The bulbs are all bad
The bulb holders are 1/2 " vs 5/8"
The cir board surface the bulb holder makes contact to is dirty
The ground to the dash frame could be failing BUT the gauges would be pegged.
There might even be a fuse in that path but I don't have my wiring diagram handy

Classiccarwiring.Com

color coded and easy to follow

as for temp and fuel both going at the same time.

there is a IVR (instrument voltage regulator) on the early As I don't know where it is mounted, might be in the fuel gauge, might be on the back of the cluster.

if you were missing a ground or had a bad ground to the cluster the gauges would peg high and burn out you gauges.

if they are both failing low then the IVR is the typical suspect.

if you replace it I would suggest the real time engineering replacement. Well worth the money.
RTE limiter - rte