get a couple alligator clips, some wire and a light bulb( a reverse light on a pigtail socket is good)... clip one alligator clip to the skinny solenoid wire at the starter itself.. the other to the vehicle frame (clear off the dirt and rust) near the starter.. connect the bulb to the lng wires and set outside where you can see it...
get in, turn the key to start position and see if the bulb lights up nice and bright..
if so, you have eliminated all of the no-start safety circuits and fuses in the low-amperage part of the electrical system..
if the light doesnt light you are not even placing power to the solenoid so the starter isnt even being "called for"
then you troubleshoot fuses, emergency door interlocks, neutral safety switches, etc...
if the light does light then your issue is at the solenoid or starter... you dont need to dismantle the truck for this test.