Clicking sound when starting truck, but eventually starts.

Or when it starts stopping all together.

 

It's the solenoid. If you can't start it by hitting it with a broomstick, then it's time for a new starter.

 

I had a “similar” situation but slightly different. It may be worth a try anyway. My mechanic diagnosed and found the ground was bad. The bad ground was to the relay panel inside the cab behind the steering wheel. He added a ground wire and I have not experienced any issues since. Mine would occasionally act like it wasn’t going to activate the starter but when I turned the key a second time it usually worked.

 

On my Kenworth t660 it would sometimes click once. And nothing not even try to do anything. If you kept turning key to start, the wipers would come on..
I changed starter, solenoid, batteries, ignition switch and even Flywheel.
It would not do it all the time, may start 10-20 times, then all a sudden a click then nothing.
Changed ground. All new finally after having to get a $500 pull start (truck holds air) I put a button and wired it up now turn key hit button it’s never failed to start. You can start with key too, sometimes until it clicks, then you push button it’ll click a time or two then start.