I have a possible explanation for the question about the fuel gauge operating backwards. The gauge normally has two magnets; the one on the left (empty end) operates at full voltage all of the time. The one on the right is in series with a variable resistor on the sender; when the tank is full the resistance is zero and when the tank is empty the resistance is maximum. The needle is connected to a vane between the two magnets. Thus it would seem when the tank is full the needle would be at midpoint but it also has a spring attached which pulls it to the right, full position. As the tank goes down the resistance increases and the magnet on the right gets weaker and the needle moves to the left. Now suppose the magnet on the right—the one in in series with the sender resistor–fails or becomes disconnected. And also suppose someone in an attempt to make a repair connects the magnet on the left in series with the sender resistor. We now have one magnet—the one on the left-- and the spring controlling the needle. When the tank is full the magnet is at maximum pull and moves the needle to empty. As the level in the tank goes down the resistance increases and the pull of the magnet is less allowing the spring to move the needle to full.
Whala, the gauge reads bass ackwards!
Andy