I went to crank my truck after a quick trip to lowes and it wouldn't start or even try to crank. I purchased a new starter solenoid and it still would crank. So I took the ignition switch cable off and shortes the ignition switch terminal to the battery side terminal on the solenoid and it started right up.

So why won't it start with the new solenoid unless I short it out?

 

That's the starter relay; the solenoid is on the starter. (And yes, any parts store that calls it a solenoid is wrong.) You didn't short the relay out, you simply energized it with a direct connection to the battery. This proves that the relay DOES work, and that the problem is "upstream". So next question is - automatic or manual transmission?

 

It's an automatic transmission

 

Try starting it in Neutral. Then try moving the shifter around between Neutral and Drive, and between Neutral and Reverse, WHILE holding the key in the START position. If any of that changes anything, if the engine cranks even briefly, then the neutral safety switch NSS, aka. Trans Range Sensor TRS, is the prime suspect. Either out of adjustment, or just shot.

Ignition switch is another suspect, as are the key cylinder and the actuator rod that goes between the cylinder and switch. When you turn the key from RUN to START, does the movement feel normal, moving the full range you expect it to?

 

Okay, so sometimes but not often it will start in park but most of the time I have to put it in neutral.

 

Check these bolts

 

I have seen a better solenoid upgrade for a 7.3 PSD but can't find it, what brand and model is it?

 

You could use a Stancor 586-902 or a Western Plow 56131-K, as is often done for the GP relay (it's still not a solenoid, no matter how much anyone tries to call it one), as a starter relay. You'd just have to ground the second coil circuit terminal. But it's irrelevant to the OP's issue, as he has already demonstrated that the starter relay is good.

 

Correct^^^^^^^ he has a linkage problem or a MLPS issue. I'm going with linkage issue

 

Okay I'm lost now. I went out to start the truck today and wouldn't start so I put it in neutral and tried and it still wouldn't start. So I tried the trick on the starter relay and can hear it clicking but it won't turn over. Checked both batteries and they have around 12.58-12.67. I got different readings at times depending on how many times and had recently tried to start the truck. So am I looking at a starter issue? Or can you replace just the solenoid on the starter?

Side note I did check the to screws pointed out in the picture and both are snugged up. I had that problem once before about a year ago and had to tighten them down then.

 

Did you hear the solenoid (the solenoid on the starter, not the relay on the fender) clicking, or just the relay?

Check the wires down at the starter.