Be careful when buying a replacement remote control for a 1999 Ford truck. It was a split production year for those vehicles. Trucks assembled in March 1999 and later used a different keyless entry remote keyfob than trucks produced through February 1999. The two remotes look very similar, but are not interchangeable.
If you have your original remote, you can tell which replacement part you need by looking at the FCC ID on the back of the case. The keyfobs used for the first half of the model year (RUI part 357-1357) have FCC ID GQ43VT4T. The remotes for the second half of the model year (RUI part 343-1343) have FCC ID GQ43VT11T or an FCC ID beginning with CWTWB1U. If you do not have your original remote or cannot read the FCC ID number on the case back, another alternative is to look for the production month of your truck on the vehicle information sticker.