The fuel PCM on a 1989 Mercury Cougar is located above the gas tank. It is on the rear fender wall on the driver's side of the vehicle. The Fuel Pressure Control Module is another way to say fuel pump.
You can replace the alternator on your 1989 Mercury Cougar by removing the alternator belt. Disconnect the wiring harness from the back of the alternator. Remove the alternator retaining bolts. Reverse the process to install the new alternator.