I moved this into a new thread as it is a separate issue.
Would be great if someone could post a schematic diagram for your truck.
By chance does your owner manual show the under hood relays for flashers/signals?
If the 4 ways & signals are tied into one flasher, could be the wires into the 4 way flasher switch or a separate relay? Check the fuse for it?
I'm sure the guys will chime in with some more ideas on this one as well.