I would say it sound like a "short" of some kind
Now given, this doesnt mean "short" to make something pop or go out, I mean "short" as in a possible arc.
It sounds like you already checked the relays (It is funny, most of HT's answer start with banging on something... dont get me wrong... he is right, just funny how alot of problem Dx with these trucks start with banging - and sometime it ends with banging... like your head against something
)
Have you checked load on your light when the headlights are turned on?
Does it change?
You have to check it all the way back.
Electrical issues are a PITA.
Also ask yourself was there any event that you might have done prior to this happening? (ie. you went for a swim?)
and Lastly and most importantly.... have you actually check the outside blinkers to see if it is a real system issue or just at your dash?
(it seems these dashs can be kinda finicky... I know HT told me something similar when my passlock light started to act up)
--- (again I have to say we are VERY lucky to have HumTech on our forum. Great guy, and knowledgeable too!!)
----- (actually I can say that about most of the guys on here!!!)