52Carl has it right. You will find once you get a good ground on the gauge, it will work as designed. Without it, all you are doing is sending full power straight to the gauge, causing it to jump straight to F. Had the same issue on my 1st truck back in the late 70's, of course I was only 15 at the time and pretty darn proud of having a "F"ull tank of gas! A week later I still had a full tank ;(
