Fuel Gauge Trouble Shooting Help Needed!!

If neither gauge works it could be several things, including but not limited to

the connector to the cluster

corrosion/ loose connections right at the gauge studs

bad / poor gauge regulator, or bad connections in the socket it fits

(DO you have a rally cluster?)

Of course the gauges themselves

And of course sender wire problems. Don't forget the temp sender wire goes through the bulkhead connector, which could be a bad connection.