I replaced my fuel gauge sending unit after the gauge read full by the ground test, and the voltage regulator on the back of the gauge pannel because my fuel gauge was not working. I now have a full tank of gas and the gauge reads 1/4 tank. Do I need to ajust the gauge or sending unit or could this be caused by something else. thx.

 

is it installed in the right position,,I changed mine and it only reads 3/4 when the tank is full

 

Changed my sending unit out a few years back on the 67 coupe. The sending unit had an adjustment screw to raise/lower the float arm. Justed guessed at the position and the gauge reads about right. If you have no adjustment screw, guess you could bend the float arm to correct for the difference in gauge reading...