4 wheel drive problems

It all started when i left the truck on the street for the winter for about 4 months.
Beforehand it would engage normally.

Now when i press the awd button on the shifter it will flash forever and never engage. Soon i realized it would engage after i would turn the car off and back on, which is the way i've been forced to use it on the beach.

Apparently the actuator is working i had a couple mechanics look at it just didnt have enough time to leave it there for 2 weeks :/

 

also when I would turn the car off and then back on the center diff lock is engaged if that makes any difference

 

You mentioned sand, it gets everywhere. Maybe a contact is dirty or fouled with sand? Is there a way to apply voltage to the actuator to ensure it's doing it's job. I don't know about that last one, just spitballing.