2008 Ford F-350 won't start

My 2008 Ford F-350 doesn’t make a sound when I try to start it. The battery is good. The steering does not lock with the key out. Is it something to do with the anti-theft system?

'‘more input’'
does a theft light flash ? ( some 08 industrial pickups did not have the pats system )
Automatic or manual ?
do the dash lights go off as you attempt to crank and back on again when you release the key…as normal ?

I can’t see a flashing theft light. Automatic Transmission. Dash lights do go off when I attempt to crank and then back on after.

Shift the transmission into neutral and then try starting the engine.

If the engine starts there’s a problem with the park/neutral safety switch.

Tester

I tried starting it in neutral and it still doesn’t start.

Since the dash lights do go off when attempting to start, I think we might be able to rule out a bad ignition switch

It also doesn’t start in neutral, so we can probably rule out the switch

“The battery is good” is unfortunately a little too vague for me. Please define good. How old is it? Has it been tested?

Are all the connections at the starter and battery clean and tight?

Seems to me the starter motor itself may be faulty. If you’re getting 12V at the appropriate starter terminals when attempting to start, you need a starter

You could crawl underneath the truck and lightly tap on the hammer, while your assistant tries to start. But only if you can safely do so.

There are two batteries putting out 12.4 volts.

A fully charged battery should be at 12.6 volts

And a bad battery will quickly drop to an unacceptably low battery when asked to do anything

That is why I asked if they have been tested

Load test
Capacitance test

Any of these would be fine

What events preceded it not starting ?
There is a starter relay and a fuse in the engine compartment fuse box…plus a fuse in the junction box under dash. ( see owner’s manual for locations )
One leg of the relay will be hot all the time. The other will be hot only in the cranking mode.

A battery at 12.4 volts is actually dead. As db4690 said, a charged battery will have 12.6 volts.

The starter isn’t cranking because your batteries are dead.

My votes the starter or relay/selanoid . Do as @db4690 said and rap the starter with a hammer to see if it’ll engage. I’m assuming you’ve tried jumping with another vehicle already. If it is the starter, if you have a automotive electrical shop in town, have the original starter rebuilt.

I replaced both batteries with new fully charged ones. I also tried rapping the starter while trying to start it.