Since you have the front tank out, do this. Take the fuel sender out of the tank, take a battery jumper cable, hook the Black lead to the battery Negative post, hook the other end to the wire on the underside of the mounting plate, turn the key on, move the float arm up and down, if the gauge don't move, then you have an open connection to the gauge, if gauge don't move, pull the connector off the FSV, jumper the FSV connector from #1 to #3, the cab switch must be selected for the front tank, turn the key on, move the sensor arm up and down, you should get a gauge reading. No reading, gauge is bad or cab switch is bad or connector to cluster is bad or the sender is bad.
If you do getting a gauge reading, then the FSV is bad.
Edit: Make sure the connector at the sensor is not corroded, since neither front or rear sensor works it unlikely.
I told you on your 1st post where to get a new FSV.