Some of the test procedures are for guys with older parts that want to know what's wrong. The procedure for new parts is to test and calibrate them together on the bench before installing. You can pull them and do that to be sure the new gauge and sender are good or try to test in vehicle. Test not guess, as Jerry would say.
From the web:
If your gauge reads FULL AT ALL TIMES:
A. Probable Causes
1. Wire from dash gauge to sending unit is broken and/or the connection is corroded (not making a good electrical connection).
2. Resistance wire inside sending unit is broken
3. Sending unit is not properly grounded to tank or tank is not properly grounded to chassis
B. Testing
1.Remove the wire from the contact stud on the sending unit and ground it to the chassis. If the gauge now reads Empty, the trouble is either poor grounding of the sender or a bad sending unit.
2.If the gauge still reads Full, touch a grounded test wire to the sending unit terminal on the back of the dash gauge. This terminal is often marked with a red tag. If the gauge now reads Empty, the wire from the dash to the sending unit is broken or the connection to the dash gauge is corroded.
3.With the sender removed from the tank, connect an ohm meter to the sending unit (one lead to the contact stud and one to the housing) and check the resistance of the sender as you manually raise and lower the arm. This reading should be 0 to 30 ohms (or very close).
4.If none of these tests finds the problem, the dash gauge is the problem and should be rebuilt or replaced.
C. Repairs
1. Make sure that a good ground is present at the dash gauge and also at the sending unit. Run a separate ground wire to the chassis if necessary.
2.Sliding contact arm may not make good contact to the resistance wire windings in sender. If you are experienced with electrical repairs you may be able to clean the wiper and resistance wire coil or replace the wire. Otherwise send the unit to a specialist or replace the unit.
3.Check for good ground at sender body and gas tank.
