Faulted 4wd issue searched but found nothing

Okay this is odd and I need to get into the shop and check some stuff but I was wondering if anyone else ever had this issue. Before the attacks start I already searched I found nothing similar and I'm not asking for step by rep how to fix just if anyone has heard or had this or has constructive ideas. After a little fun in the mud a week ago 4wd indicator is flashing. Wasnt doing it till the next day. It's been washed. 4wd wont engage, but strangely if I shut it off turn the dial to 4hi and then start the truck I'm engaged...shut it off no light. I know about all the actuators and my theory is the ADD up front got wet, but it still odd that I can start up in 4wd and bingo....