Why is the theft light keeps flashing when i turn car on

Once the theft deterrent thinks the security has been breached, it will not allow the car to be started.
You might need to have the dealer re-program processor.
Hope this helps.

Ford have red tags on the key fob which is required to turn off the immobiliser if you have a door or boot key I.e.a second key without a red tag it does not switch off immobiliser and anti theft light remains on.the key fob "talks" to the receiver which is housed ig the ignition switch and or ecu .you will need a replacement key fob which needs to be program by an auto locksmith.average cost is about £75 per key. eBay for the key auto locksmith via google search or yellow pages.

You need the key fob to start the car