I'm assuming you've made sure the fuses for the 10amp turn, and the 15a hazard/horn fuse is good. The flasher relay should be located hanging from a brace, up above the accelerator pedal, in that area. It should be labeled flasher on the box itself.
Has any other work been performed on the truck, such as maybe a radio install or anything like that? You'll want to also make sure the hazard switch is good and plugged in, because the turn signals feed through the hazard switch.
Check for power (with key on) at pin 2, green wire at the flasher relay. And make sure you have a good ground at the flasher relay at pin 3, white/black stripe. LEt me know what you find.
The hazard switch is the first main part of the entire circuit. The 10amp Turn signal at the integration relay (fusebox in drivers kickpanel) fuse feeds pin 10 (green with black stripe) at the hazard switch. This wire will only have power with the key in the ON position.
The 15 amp hazard/horn fuse (under hood fuse box) runs a blue/white wire to pin 8 at the hazard switch. This fuse should have 12 volts always. These are the 2 wires you are concerned about first and foremost.
The green (pin 7) and blue/red (pin 9) feed from the hazard switch to the flasher relay. The blue/red also feeds to the turn signal switch. The green/black and green/yellow in pins 5 and 6 respectively, feed FROM the hazard switch to the turn signals and dash indicators. But everything originates from the hazard switch.