Reach up on top of your gas tank and unplug the cannon plug from your sending unit. Turn on key. If guage goes to full sending unit is bad or float is full of gas. I had the same problem with my 96 Ranger and found the float(brass barrel type) was full of gas due to a hole worn in it from the arm it was attached to. I opted to just replace the unit since the truck had 86k miles on it and didn't want to have to have to drop the tank again any time soon. Easiest way to replace the sending unit is to pull the bed bolts and slide the bed back but on mine that wasn't an option as I have a fiberglass toneau and a Ford bed liner in it. In my case it was easier to drop the tank and that was a bear to do without help. Getting it out wasn't so bad...it was getting it back in that sucked. Hope that helps, Carl