How do you repair the amount of fuel indicator on 1986 Mercury Grand Marquis?

The sending unit for the fuel level is located in the fuel tank. Basically to change it you have to drain fuel, remove the tank, then remove & replace the sending unit. You might try www.autozone.com under vehicle repair guides to see if it covers removal of the tank on your specific vehicle. The 1986 Mercury Grand Marquis fuel tank, like many Lincolns of that ilk, is a vertical tank in from of the trunk and behind the axle. The sender/fuel pickup is mounted on the front of the tank and can be accessed easily, with proper clearance for work, from below. You may remove the tank, but that is not easy. Using care and proper tools to prevent sparks, remove sender line, unlock the lock ring tapping gently counter clockwise, remove the sender, and replace with new one, taking care to place it as close to vertical as possible. Replace lock ring. This is the best I can remember. The sender is an approximation anyway and can not read exactly. This will work if the instrument panel needle gauge is working properly. Usually, it is. Oh, and important, no smoking while working on this repair. Chewing and dipping allowed.