A 92 Mustang uses an EEC-IV computer setup, you can get the simple code
reader that blinks an LED and/or tone to correspond with the trouble
codes it is transmitting very cheaply. A code reader for these vehicles
is cheap enough that is a great diagnostic tool for the hobbiest.
Some of the most common check engine light symtoms for these cars is
the EGR position sensor or TPS sensor.
The self test connector can be found right next to/below the windshield
wiper motor on 1986 to 1993 Mustangs.