I have a 66 GTA with a very frustrating issue. When I bought it the fuel gauge would read only about 1/2 full with a full tank. I bought a new sending unit-hooked it up outside the tank and the dash gauge worked as it should. Installed the new unit and the false reading still exists. I am on my third sending unit plus I just installed a brand new tank with no soloution. I have checked all the grounds ( firewall to engine, gas tank to frame and sending unit to tank) and when I ground the sending unit wire the dash gauge reads full. I read that the constant voltage unit behind the dash has nothing to do with false readings yet looking at the wiring diagram the circuit passes through it. Could that be my issue?