Yesterday my truck (97 F350 7.3, 5sp) decided it won't want to crank once it gets warmed up. It was intermittent at first and now it's happening more frequently.

I replaced the solenoid on the fender and it again cranks as normal when cold, but after a short warmup drive, and shutting the engine off, it won't crank.

The lights dim on the dash as normal, so it seems like power just isn't getting through. I'm stuck in South Dakota on vacation at the moment because of this so any pointers would be helpful.

 

Could be a bad starter.

 

It appears to be a recent replacement, an ac delco. Of course that doesn't mean its flawless.

Is there any easy way to check it?

 

You can take it off and have it tested. I've crawled under the truck and smacked them with a hammer to get them to crank, but that's just a roadside test LOL!

 

I have a small test light that I'll use to check the solenoid. If I remove the starter and take it to a shop then it'll cool off, and the nearest shop is 35 miles away.

 

You can do the same test that a part store does with a battery and jumper cables.
The part store test doesn't put a load on it.

 

Starter is good. I jumped the solenoid and cranked the engine when the key wouldn't crank.

Right now I'm looking at the neutral safety switch. I have cruise control so I'm not sure how that would affect things (cruise is disabled when the clutch is depressed).

I understand you can bypass the switch which I assume you can do by sticking a wire across both plugs? I'll wait for confirmation before proceeding.

 

It sounds like the heat is causing a bad connection

 

There's no neutral safety switch. There's a switch on the clutch pushrod, that's actually two switches in one. One switch _opens_ when you first start to move the pedal; that's what interrupts the cruise, the two terminals closer to the seat are for that switch. The other switch _closes_ when the pedal is near the floor; that's what energizes the starter, the two terminals closer to the firewall are for that switch.

If by "lights dim on the dash", you mean the illumination lights, then that means there's a draw somewhere. That would suggest that the clutch switch is working, and either the relay, the solenoid or the starter are drawing current. If you're just seeing the indicator lights go off, that's just the normal operation of the key switch, nothing to do with current draw in the starter circuit.

Simple narrow-down test - pull the small wire off the starter relay and stick the red probe of a voltmeter in the connector, black probe to battery negative. Have an assistant turn the key to START. If it shows voltage, the clutch switch is good, and the problem is downstream (relay, starter, wiring). Are you sure the fender relay is mounted firmly to the fender? It completes the coil circuit by grounding through the mounting plate.

Heat could be causing the solenoid on the starter to fail, or the motor itself. Problem is, to bench test the starter, you'd have to do it right after driving the truck while it's still hot.

 

Which relay is the starter relay? I see 7 of them and the case box cover just has a relay number, but no mark stating what each one is. The previous owner was not able to provide an owners manual.

Again the truck will start if I bridge the starter solenoid even when it acts up. I'm sure the starter is fine because of that. I'll try checking the relay like madpogue said once I can figure out which relay to check.

 

The starter relay is mounted on the passenger side fender. It will have several wires on one large post post and just one wire on the other large post, then there will be one small wire on one small post. This small wire is the one you test to see if you have voltage when you turn the key, with the clutch peddle depressed. If you get voltage there when the key is turned, and the clutch pressed, the clutch safety switch is good.

 

I thought that's the solenoid, not the relay

 

The solenoid is on the starter. The relay on the fender triggers the solenoid.