Stop and turn signal issue

First thing I would do, plug it into another truck and see if the problem repeats. That will narrow it down right away.

Then,

Check all fuses and plugs. I just replaced my 2YO female 7pin on the truck, completely corroded. My new one, I covered all connections in dielectric grease, then completely wrapped it in electrical tape, followed up with gorilla tape. Yes, that is over top of standard plastic cover supplied with the 7 pin plug.