If it isn't as simple as pulling the door open then there should be a button inside the glove box that you will need to push. If that doesn't work anymore then inside the trunk there should be a pull handle to release it as well. If the button doesn't work and you aren't afraid of people stealing your gas then i would suggest once you have it open, remove the tab that latches it closed. This will make it easier to open from then on... Simply open it from the outside.
According to my Chilton's Auto Repair manual : For a 1991 Mercury Topaz ( front wheel drive ) ( 15.9 US. gallons )
it will be in the fuel tank.
It's in the gas tank.
Tank size is around 60 to 65 Liters.
Inside the fuel tank.
In the gas tank.
15 Gallon except on all wheel drive.
According to my Chilton's Auto Repair Manual : ( A 1991 Mercury Cougar has a 19.0 U.S. gallon gas tank )
It's in the tank.
check the fuel pump and sending unit in the fuel tank
According to my Chilton's Auto Repair Manual : A ( 1991 ) Mercury Cougar has a ( 19.0 US. gallon gas tank )
Time to change the pump. But a " 73 ? Maybe the pick-up is blocked. Have to drop the tank to check it out.