Diff wont lock up??

Ive got a 99 tacoma with the off road and locking rear diff package. When i bought the truck about a year ago i never had a problem locking and unlocking the rear diff. Now the light just flashes at me?? Any possible problems/solutions would be greatly appreciated

 

Truck has to be in 4 Low for Diff to lock up.

 

He said it used to work fine so he probably knows to be in 4L. OP I would check the actuator

 

Same situation as me, but I forgot it had to be in 4 Low, just last week.

 

I forgot to mention that i have the grey wire mod also. I should be able to lock it in 2 wheel if i wanted. Just out of curiosity I am going to go put it in 4 low to see what happens today

 

Well that shows that I shouldnt assume. I would def try in 4L to see if it is an issue with the Grey Wire mod. Good luck