FORD 2013 E-450 v.2 - Manual (Page 65)

If the key was not successfully programmed, it will not start your
vehicle’s engine and the theft indicator light will flash rapidly. Wait
20 seconds and repeat Steps 1 through 8. Take your vehicle to your
authorized dealer to have the new key programmed if you are still
unsuccessful.
Wait 20 seconds and then repeat this procedure from Step 1 to program
an additional key.
64 Security
2013 Econoline (eco)
Owners Guide gf, 2nd Printing, November 2012
USA (fus)