What year is the mustang? Also you need a remote from a vehicle 1998 and up. In 1998 they changed the RAP modules frequency. Pre 1998 they actually had an external antennae with a plug exactly like the one on the back of your radio. In 1998 they change the frequency to allow a more compact internal antennae. Explorer key fobs are the same as Rangers, they have to be because the RAPS modules are the exact same. Hell, Rangers RAPS can even be wired up to a 5 digit keypad just like the Explorers, they even have the default 5 digit number stamped on the label. You have to pull back the black foam around the box to see this.
Quality Engineer (Electronics) for Kia Motors
University of Tennessee Electrical Engineering Graduate
2000 XLT 2.5L A/T