If you are pulling the harness from a junked truck you’ll want to start at the throttle body and follow the wires to the fuse block and to the firewall. You’ll have to pull part of the harness from inside the truck through the firewall. This bundle of wires follows down to the firewall grommet. You will need to remove and pull the interior wiring through the waxy weather-seal material and plastic firewall plug with hot water or a heat gun. You will trim most of the wires out of this plug. Take your time. When in doubt, follow a wire to its end before cutting it. Chances are one way or another you’ll have to make repairs to any harness, but that’s not a big deal.