FORD 2013 E-450 v.1 - Manual (Page 65)

If the key has been successfully programmed it will start the vehicle’s
engine. The theft indicator light will illuminate for three seconds and
then go out.
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.
Security 65
2013 Econoline (eco)
Owners Guide gf, 1st Printing
USA (fus)