Just to make sure I'm reading this correctly, the starter motor doesn't crank the engine over correct?
Do you have access to a voltmeter? We should be able to do some basic checks to get to the bottom of the issue.
Also could you let me know the year, and if your truck is equipped with a standard or automatic transmission?
Lets do some simple checks first.
If you haven't already, shift the transmission to neutral, and see if it'll crank (just a quick way to check transmission linkage adjustment). If it starts, then it's time to check the linkage out (it's a long shot but worth checking).
The easiest way to do the testing is at the starter motor relay in the fuse box under the hood. Pull the relay out, look on the side or bottom and it'll call out the pin numbers.
Using your voltmeter check for the following voltages at the pins (with the relay out);
Pin 86 - 12 volts only when the ignition key is turned to the start position
Pin 30 - 12 volts all the time
Pin 85 - with the key off, check resistance between this pin and the battery negative terminal
Let me know the results and that will help us narrow down what part of the system is at fault.
I've got to post this as an answer, but please don't click accept until we get to the bottom of your problem.
Good info, here's what it tells us...
Ignition switch is good, neutral safety switch is good, and you've got power to go to the starter solenoid..
So, the next step is testing the ciruits to the starter.
The big heavy connector 12 v all the time obviously
The small terminal, 12v with the key in the start position
If they both check out OK it's time for a voltage drop test... Put one lead on the lug the heavy wire connects to at the starter and one on the positive battery terminal. Try to crank, watch the voltemeter and let me know what you get for a reading.. It should be 0v, if you see 12v you've got problems with the heavy wire or it's connections.
I'm assuming the starter does nothing correct? No click / thunk / any type noise?
Only 10 volts at the small terminal, that's a bit strange..
That tends to make me think there is some stray resistance in the wiring between the starter relay and the starter itself, but it should still be enough to operate the starter motor.
I would attatch another wire to the small terminal and run it up near the battery.. It would be best to fuse it if you've got a fuse holder laying around.
Jump it to battery positive and see if the starter cranks over.. Just make sure the truck is in park + parking brake set so it doesn't take off on you. Be prepared to quickly pull the wire away, if there is a short in the starter it'll get real hot, real quick!
If the starter won't operate by jumping it like this, the new (remanufactured?) starter has gone kaput on you (assuming the truck batteries are fully charged) because at this point your elimnating all the truck circuits.
It's not uncommon for reman starters to fail in short order like this, they tend to bench test them, but that doesn't put an real load on them (like your Cummins engine does anyway!). I suspect you've got a new, bad part. Take a wooden hammer handle or the like, and tap on the starter solenoid while a helper turns the key, it might 'jar' it back into existance enough for it to operate.
Try it and let me know the results.
The part should have a warranty I would imagine. I'd print this whole thread out and bring it as proof that you did a complete diagnostic on the starter circuit (you did a fine job!). We know everythings working, but the starter.