Ford did not equip the 5.0 Mustang with Mass-air flow until 1989 (1988 in California).
Unless your stang has been converted (senser is connected in the middle of the air-intake tube right before air filter), it is run by speed density. Your "MAP" sensor is located on the upper part of the driver-side firewall.
Welcome. Searching can be helpful. And in the event that searching doesn't cover what you desire, a brief, punctuated synopsis can be quite helpful. Knowing the year and milage, when the issue arises, if any new parts or work was done around the same time, etc etc are all helpful.
In general, a bad ground for the gauge cluster can create some issues.