/\ /\ /\ Pretty sure that will be your issue up there /\ /\ /\. On my factory locker, the light will remain flashing when you press the locker switch until the locker actually engages, then it goes to a solid light. While it's flashing, keep doing S-turns to help it engage, and if you're already into a situaion, be super gentle with it until it goes solid.
Without the limit switch to tell the ECU that the shift collar is actually engaged, it will assume it's still waiting for the teeth to get in the right spot on the collar to engage and keep flashing the 'in progress' light.