hi..I just replaced my ignition barrel and to my horror discovered that my car would not start....I was told I would have to have my new keys programmed by ford at a cost of over £150(including two extra keys) any way I understand that the pats.(alarm) unit transmits a code which is passed by the Key..and authorise the engine to start..so..
if you have your old key fobs simply remove the transmitter from the fobs and replace in the new fobs..and hey pretso..no cost
1.the transmitter is located under a red cap on the key fob..
2.remove the cap from your old fob to gain access to the transmitter(like a glass capsule..)so be careful.
3.do the same to your new fob..and swap over the transmitter and you will be running again wthin no added expence..do this with all the keys you have.
Kevin.B(electronics engineer), August 2009