Try turning on the key and jumping from the pos. on the battery to the starter solenoid. If no response from starter, And starter is good, then the problem is most likely in the ground. Ground starter with  a battery jumper cable and try again. If major arc is present then Solenoid or starter is shorting out. Can't be to much of anything else. if starter turns, then you can start the truck by turning the key on prier to jumping the starter. If it's a no start, then that's another system.