A dipstick is the most common way to measure the amount of oil in your Mustang's transmission. The dipstick is a thin metal strip used to measure the quantity of oil that is in your Mustang's transmission. The dipstick will usually have maximum and minimum marks to show the range which the oil should be within.
To check the transmission oil level on your 1983-2004 Mustang you will need to crank the engine and drive around until it is at normal operating temperature. Once at operating temperature place your Mustang on a level surface, put it in park but leave the engine running. Pull the transmission dipstick and wipe it clean, then stick it back in, pull it out and take the reading.
If you drive a 2005+ year model Mustang you will need to take it to the dealership or a transmission shop to have the fluid level checked.