gas gauge

If the blue wire was shorting to ground the needle would peg on full. Most likely you have a loose connection somewhere that opens the circuit occasionally as you drive. If there is gas in the tank and your needle moves between empty and whatever level of gas you have in the tank, you might check to make sure the connection to the sending unit is clean and making a good connection. In addition there is a connection for that wire behind the driver's kick panel and then again at the connector on the back of the instrument panel. Make sure all those connections are clean and solid.