1984 Other Ford Models GAS GAUGE FAILURE

As this is a motor home, it may have two tanks. If you changed the sending unit and it didn't fix it, it may be the guage itself. But you culd have a pinched wire or bad ground on the tank causing this. Checkto see if you have a good ground going to the sending unit and then check and see if you have the correct power going to it. Also if it used the same float in the sending unit it may be partially full of fuel causing this. If this is the added on tank or if it has one, check that for junk as the manuacturers leave those outside alot and the get junk in them.