What would be the problem if you try to start the truck and it just clicks.

Check that the battery connections are clean tight and secure. Make sure the engine ground cable is good. It could be a voltage drop in the electrical circuit but is more likely the starter solenoid or starter has failed.

If you try to start your truck and it just click check that your battery is fully charged and battery cables connections are making good contact. If thats not it try replacing starter solenoid.