Make sure the truck is in park or out of gear before doing this:
Carefully with gloves on use the handles of a pair of bare metal pliers to bypass the starter solenoid. Put one handle of the pliers on the large post on the solenoid and the other on the (large) post that has the wire that leads to the starter. This shorts across the solenoid and will trigger the starter. ( Hence why it needs to be out of gear )
Be careful the pliers may get very hot if the starter is bad or shorted. If the starter operates normally it's a bad fender solenoid, replace it.
Parts stores will check the starter for you if you take it off. Make a note of how the cable goes on the starter. If you don't, it can take a while to figure it out.