How do you repair a 1993 Mercury Cougar gas gauge that stays past full all the time?

the sending unit is nothing more than a float in the gas tank. Check in the trunk first and see if you can access the sender from there. you will have to pull the carpet up. If you can,you should be able to disconect the electical plug-in sending info the the gauge. try that. It can only be the sending unit or the gauge itself. I would start by pulling the power to each one.