Classic/Antique Car Repair: fuel gauge 67 350 Camaro pegged past full, fuel gauge, frame rail

Question
what causes the fuel gauge to go past the full mark when key is on? I have replaced float & sending unit in gas tank and made sure I have a good clean ground on frame rail.

Answer
Jimmy;
Hi  do you mean it is broken or it only does it when it is in the on setting / and it will work right when running ?

if it is ok when running , and it only does it in the on setting- that is the way it is.  it goes into its normal working mode when running , so it would not burn out if the key was left on. It would be nice to have it full of gas all the time hua ?
Roger.......>><.