My 2001 F250 7.3 diesel has been having intermittent starting issues. Sometimes it will start up as normal but occasionally it just makes a clicking sound. I replaced both batteries today and just "click." I put it in neutral and it started right up. Put in park and switched on and off several times and it fired right up. What would be the likely reason for this?

 

There could be a few reasons among which are the starter itself, the connections at the starter and the battery cable connections at the engine.

Here is how you determine which it is.
Turn the headlamps on, have some one watch the headlamps as you attempt to crank over the starter.
If the headlamps go dim, there is a poor connection from the battery to the engine or starter.or the starter needs to be replaced.`
If the headlamps don't show any change, either the starter relay is defective or the starter has a temporary open inside it, which could be worn brushes . In that case sometimes a slight tap on the starter housing will allow them to move and make a better connection and it will start a few times, but the starter should be replaced anyway.
Don't forget that starter has been on there for at least 20 years and many starts.
Better to change it at your convenience than in an emergency.
If you require further assistance , please don't hesitate to ask.
Thanksgiving came and went, so Merry Christmas !!

 

After several hit and miss starting attempts, After , I went to the parts store and bought a new starter for less than $300. I've never replaced a starter but found it to be a much simpler job than expected. There was only two bolts, rather than three that some have and only two wires. When I handed the guy at the parts store my old starter, he said "yeah, one of them has sheared off. I assume it meant one of the teeth on the spindle. I hadn't noticed. Since I installed the starter, it has started every time. I believe it is fixed but I'll post a follow up if I get stranded somewhere Merry Christmas to all!

 

Thank you for the update.