4Lo flashing randomly

I saw a few threads about this but not a real solution. Anyways, havent been driving my truck lately and went on a weekend trip with it. Went to come home today and when I started it, the 4Lo light just blinked, on the dash. I havent used 4wd recently and wasnt attempting to turn it on today. After I noticed the light flash, I tried 4Hi and 4Lo. It didnt seem like anything happened. I knew it was still in 2wd, so I just drove home, rather than risk getting stuck in 4wd. Got home, tried turning the knob and nothing. Any ideas? Ive seen anything from a plug behind the rad that could be disconnected, to possible actuators needing replaced. I feel like it wouldnt be actuators, unless I was attempting to get into 4wd?

 

Also read a few things on other sites that the vacuum line may have cracked/be leaking somewhere. Im thinking something like that may be more likely than an actuator, just with it coming on w/o even trying to engage the 4wd. Just wondering if anyone else has experienced something similar, to help narrow the possibilities. Thnx.