the gas meter needle goes back and forth as I drive car. why/

...again am going to insist that the main ground connection gets renewed (metal to metal) because there is a blue high-amperage spark that creates a layer of corrosion that does not matter to a higher amperage requirement, but more delicate requirements such as the dashboard cannot tolerate varying available amperages and reduced voltages~ .....see the varying voltages are at the entrance to the component voltage regulator....the fuel gauge works off of variable resistance, which if issued varying voltages will produce varying results.....garbage in...garbage out~

a wrench (to take the bolt off) and a wirebrush the lug and the ground to establish a comfortable high-amperage connection~