92 mustang LX started beeping when started

[daysleepin]

Sounds to me like you have plugged in something that does not belong to that year of car.

Do you have a gas gauge that does not work?

My son once had a 91 LX 2.3 that had that beeping thing going on and
the gas gauge did not work. So we replaced the whole instrument cluster from a known 91 parts car and both the the gas gauge started working and the beeping went away. The previus owner did admit to replacing the speedo cluster when the speedometer died.

We suspect his replacement came from the wrong year