I bought my Heritage used and with a full tank of fuel. I began to think that this bike got fantastic milage but realized that the needle sticks on "F". I lifted the gauge out of it's resting place but the two wires are buried within another chamber under the speedometer. Where is the sending unit for this gauge and can this be corrected without buying another gauge? The needle swings from "E" to "F" when the ignition is energized but it stays there. I just added 3.5 gallons to the tank yesterday and it was still on "F". Any help?