http://www.coolcats.net/tech/troubleshooting/heatercore.html
1988 cougar will not crank over
To change the heater core on a 1988 Mercury Cougar, first ensure the engine is cool, then disconnect the battery. Remove the dashboard and the center console to access the heater core housing. Disconnect the hoses from the heater core, remove the mounting bolts, and take out the old core. Install the new heater core by reversing the disassembly steps, reattach the hoses, and reassemble the dashboard and console.
The 1988 Mercury Cougar diagnostic port can be found under the hood.
A "heater" or a "heater core"?
inside of the tank
According to one of the Ford websites : For a 1988 Mercury Cougar , 3.8 liter V6 engine : ( the spark plugs are gapped at .054 inch )
According to one of Fords websites : For the 3.8 liter V6 engine in a 1988 Mercury Cougar : ( the spark plugs are gapped at .054 inch )
Well, you don't state the poblem, but if all your turn signals are not working and flashing as they should, replace the Turn Signal Flasher Relay.
driver side footwell under dash.
For a 1988 Mercury Cougar : According to my Chilton's Auto Repair Manual : For the 2.3 litre turbo ( 18 U.S. gallons ) For the 3.8 litre V6 ( 21 U.S. gallons ) For the 5.0 litre V8 ( 20.7 U.S. gallons )
.054 inch ( according to motorcraft . com )
You failed to list if it is a V6 or V8. Click the link and then choose the correct engine.