Flashers don't work.

Check fuses , check wiring for obvious problems , you can't see electricity you need a multi tester to see what has power/ground and what don't

Trucks have a particular problem with electronics outside, in the rear. When you drive, dirt & moisture tend to get thrown up into fenders and bumpers, and that eventually gets to the ground wires. So check the ground wires for the signal lights. If the rear don't work, it's likely the front don't either. You can attach a wire to the frame as a test ground and touch that to all the ground points at the lights.