[grovesmr]

You will need a complete circuit. A ground wire may not be needed IF the screws holding the sending unit have a good connection to ground from the unit to the tank and the bolts from the tank have a good connection to the frame. If all these parts have been painted you may not have a good connection.

You can test the sending unit with a voltmeter, you should see resistance change as you move the float arm. With your leads connected to the two contacts on the unit.

If the unit checks out make sure you have continuity to the frame when the unit is installed in the tank from one of the contacts.

If original unit didt have the extra lead that this one does. You can send the ground to anywhere convenient. If original didn't have that extra lead its assuming ground through the unit>tank>frame and replacement may have the unit isolated from the flange which is why it has a separate ground lead