This is on a 1995 F150 XLT extended cab. The key less system is the dealer installed re-branded code alarm key less entry and alarm. There's a small button used for valet mode.

Turn the ignition on and hold this button down. After about 20 seconds the siren will chirp a few times and the door locks will cycle at the same time. Keep holding the button down and press the arm button on the remote. The doors should lock. Let off the button and turn the ignition off. Now try to lock and unlock the doors with the new remote. You should be good to go.