What might be the problem with my fuel gauge in my 1966 Mustang?
it sounds like the sender unit to me. next time you know that your fuel level is low, remove the sender from the tank, and check to see if the float arm is moving freely. because it's an old car, moisture in the tank can cause the arm to seize up a bit. this is a common problem and this part can be bought brand new from many mustang parts suppliers, and can easily be swapped in a matter of minutes if you're familiar with it. in case your wondering where it is located on the tank, it is towards the front of the tank, underneath the car, with a single wire (yellow from memory) running from a hole in the boot floor to it. and remember, the fuel level has to be low before removing the unit, or you will lose a lot of fuel from the opening when you remove it. (some tanks have a drain plug fitted which can make the job a lot easier) hope this helps.