Hi and thanks for using 2CarPros.com.
Since the truck eventually starts, the battery is good which in turn indicates the alternator is doing its job. So, that leaves either a bad connection from the battery (ground or positive) or the new starter has a bad solenoid. Take a look through this link. It describes what the result of corroded, loose battery cables can do. One of which includes everything turning on but not cranking or losing power when trying to crank. Forward the link to your son or you can tell him this. It is a good starting point. It is very easy to leave a terminal loose when installing a battery or one of the connections on the starter.
https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked
If the connections are good, the next thing I would recommend is to check the starter. Trust me, I have installed a lot of them only to have the new one go bad within a few days. Often times re-manufactured ones give the most trouble. Here is a link which describes how the starter works. It shows the wires to it and explains what each one does. What he could do is this. Have a helper turn the key to the start position (when it is not working) while he checks for power to the smaller solenoid wire. You could also forward this link to him or explain it. If he finds there is power to the solenoid wire when the key is in the start position and the starter does not engage, it sounds like the starter is bad.
https://www.2carpros.com/articles/how-a-starter-and-solenoid-works
The information I listed is a good starting point to diagnose such an issue. I hope it is helpful. Please let me know if you have other questions or need additional help.
Take care,
Joe
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Sunday, July 29th, 2018 AT 7:01 PM