Fuel gauge and sender compatibility.

Original gauge and sender operated on 80-10 range. 78 ohms wouldn't cause a noticeable needle movement so that isn't/wasn't a test. 73 ohms lifts the needle to the first empty hash mark. This test shows working and it also serves as low fuel warning. Should be 3 or so gallons in the tank, depending on which tank and angle of the tank. Does your aftermarket gauge needle fall to a home position below empty at switch off? If it rests on 'E' and that is 73 ohms, 5 gallons wouldn't lift it much.