What type of truck is this?
If it is a single hard click each time you turn the key the starter is going out and will need repaired/replaced.If it is a single hard click each time you turn the key the starter is going out and will need repaired/replaced.
Double check the battery cables at the battery and at the engine, be sure they are clean and tight.
One of a few things depending on the click. If it makes consecutive clicks when you turn the key (click,click,click,click) then the odds are the battery is dead or in need of charging and there just isn't enough charge to fully engage the starter and turn over the engine. If it clicks just once, the selenoid is usually bad, or the starter is "locked" and will need to be replaced.
the loud click happens when you dont have a good connection at the starter you are grounded off somewhere down by the starter
It may be possible that the wire connections on the starter or battery are broken or corroded. It could be your starter relay. Or your starter should be tested to see if it needs replaced.
Broken starter drive? Broken tooth on converter/flywheel?
If you know the battery and all connections are good, and hear a click when trying to start the car, then remove the starter and have it tested at any auto parts store.
Probably starter solenoid switch
You have a loose wire/cable connection or the starter solenoid/relay swicth needs to be replaced.
resistance somewhere in starter circuit
Either the battery is bad or the connections at the battery or starter are corroded or loose. Was the starer bad to begin with?, Can the engine be turned over by hand? Did you buy a cheeseball starter motor like ones autozone sells?
It could be a starter problem....can you tell where the click is coming from? is it the started clicking, or a relay clicking?