Fuel pump relay is stuck. Replace it.
When making changes to a car engine it is important to have a diagram. The 1992 Ford Mustang Engine diagram can be found in its maintenance manual.
The compression on a 1992 Ford Mustang 5.0 is 9:1
http://www.veryuseful.com/mustang/tech/engine/
Your 1992 Ford Mustang GT has the 5.0 liter V8 engine with dual exhaust so it has ( 2 mufflers )
According to fordparts.com the 1992 Ford Mustang with the 5.0 liter V8 engine takes the ( Motorcraft FA-1042 ) engine air filter
.054 inch
This engine only has four spark plugs. this is wrong the 8 spark plugs going in the only head that has the engine 2.3. the oldest mustang have different engine
in the engine and they move up and down when it is running
The 1992 Mustang LX 2.3 liter, 4 cylinder engine had an increase of horsepower to 105 due to two sparkplugs per cylinder. The V8 model had a rated horsepower of 225.
According to www . ford parts . com ( no spaces ) The spark plug gap for the 2.3 liter four cylinder engine in a 1992 Ford Mustang is ( .044 inch )
I believe that is ( 5 ) U.S. quarts with engine oil filter change
10 degrees BTDC ( unless engine compartment decal shows different )