If you have dome lights and the truck will start its either a fuse or wiring. The truck should have several fuses for switched or unswitced accessories should be labeled sw acc or unsw acc
My light switch is needing some attention this weekend. Can't dim the lights and just run clearance lights. Must have a bad ground in the marker only position. I went to dim my headlights coming into the truck stop tonight and you could hear it arcing and everything was flickering. Luckily headlights side of the switch is holding up. I'll clean it up, and check the contacts. Hopefully it's a quick fix.
Seems to be the trend. They'd probably replace your ECM, then say. We couldn't find the problem, want us to keep replacing parts till it's fixed?