Being both Gas and Temp I think your Voltage Limiter (behind your cluster) is not grounded correctly or shorting out.
The Voltage Limiter is a device that takes the voltage from the battery and turns it into a series of brief voltage pulses. The periods of on time is short and the off time is long. By pulsing the voltage, the sending units can remain cool. If the voltage limiter would fail, it could cause both gauges to completely fail and not move off the left peg or...
The limiter could also be shorted, this would cause the gauges to go all the way to the right at the same time the steady voltage would could over heat the sending units.
You could try a fix by trying another one or pull it off the cluster and put a piece of paper between the limiter's pins and cluster to ensure there's no short on the cluster.....however, make sure all pins are in contact. Also...ensure your cluster is ground!!