This is the truck in your sig pic??? That thing doesn't need a heater. It's already too frickin HOT!!
I'd check the fuse, the switch, & the relay, & if those are good, then it's time to attack the blower motor resistor. Check the first 3 very carefully cuz you don't want to get into the resistor if you don't have to. They're kind of a PITA to get to.
**Check them all for power in & out. If you have power everywhere, then the resistor is most likely the problem & is probably scorched.
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