Hello, I have a 1996 F350 Uhaul box truck with the 7.5L RWD
I have run into an issue where the key no longer starts the car, I replaced everything I could think of
Ignition switch
Lock cylinder
Neutral safety switch
Solenoid
Battery
Starter
I also checked every single fuse and tried my best to chase down the wires but nothing has come up. I tested some voltages; at the solenoid that is mounted in the fender I checked for voltage on the S terminal when the key was held in the start position and there was nothing, I also checked at the Neutral Safety switch and there was voltage going through the connector from the key to the starter feed. I am able to get the truck running by bridging the solenoid but I learned the hard way that the starter doesn't disengage so it blew up in a big ploom of white smoke. I have no clue why that could be happening, I checked again after I replaced everything and the starter is still getting hot and not disengaging.
some things to note, the key was working fine when I bought it, then I was flushing the transmission to try and fix the slipping issue, I did so by disconnecting the hose that goes into the tranny radiator and turned the truck on in neutral as I added more fluid to the dip stick hole, while it was draining the truck stalled out and then the key wouldn't work so I went down the rabbit hole of replacing everything. I believe the transmissions is currently over filled. I would love if someone could help me figure this out, I have been at it for weeks trying everything I can think of.

 

If you have no power to the S terminal when the key is turned, and you do have power in and out of the NSS, then you have a break somewhere on that circuit between the NSS and the solenoid.

 

Would that explain why the starter stays engaged after bridging the solenoid?

 

Is the starter staying engaged because there is 12 volt power going to it ?.......... Or ......... Is the starter staying engaged because there is something mechanically keeping it from disengaging?

Where did you get the replacement starter?

Hobo

 

I got the replacement starter from carquest, it is my second one that I got from there, the first one blew up after staying engaged for 10 minutes and me not realizing, the second is the exact same one, it is not a remanufactured one. I have not yet tested if the starter is continuously receiving the 12v signal to the little wire, but it could possible be a mechanical thing preventing it as well, most of the shielding for the flywheel is gone and the only piece left is the one where the starter sits on, but I made sure to tighten the bolts down tight. The flywheel doesn't look damaged in any way. I am not sure though.

 

Either the fender mounted solenoid or the solenoid mounted on top of the starter is stuck and not disengaging. As a troubleshooting measure I would disconnect the small wire that runs down to the starter from the fender mounted solenoid.

 

Disconnect the small wire and then try to bridge the solenoid?

I am currently about an hour from the truck, but I will probably be there later today. While I am there I will try that and I will also look for a break in the wire coming from the NSS as well as look for any mechanical blocks, I will also get the starter tested. The solenoid i have on there is the third one I got and all I tried with that one is to turn the key and nothing happened. Also I will check for 12v at the small wire on the starter when it is running.

 

I was thinking the starter is engaged and stays that way. If that is the case, the signal to engage the starter is coming through the fender mounted solenoid(sticking) or the signal to engage the starter is through the solenoid on top of the starter(also possibly sticking). If the starter is engaging anytime the battery is hooked up, unhooking the fender mounted solenoid would tell you which solenoid is bad.

 

That is the weird thing, it only sticks while the truck is running, after I turn the truck off it stops, it only stays engaged after I bridge the fender solenoid and the truck successfully starts, I believe it is staying engaged still because i felt it after starting it and turning it off after 1 minute and it was hot before anything else got hot.
i just had a thought, could this scenario happen if the other wires coming from the alternator to the fender solenoid were accidentally swapped? But you said I could unhook the fender solenoid? While it is running or before i try and start it?

 

I see what you are saying, you need the wire hooked up to start it. You could unhook the wire and when you go to start it simply touch the wire to the other side of the solenoid and pull it away when the engine starts. Careful you may get a spark but it shouldn't be too bad. Or you could use a remote starter switch to make the whole process a little cleaner.

Another thought I would unhook that little slip on wire from the fender mounted solenoid. that just gives you the feed to engage the starter when it is working normally. It's possible it could be sending a signal to the solenoid through the ignition switch when the engine is running. That wire does no good hooked up right now.

 

I need to know what you mean by "bridge the solenoid". You should only be putting 12V+ to the S terminal until the truck starts, then remove it.

I say get the 12V+ to go to the S terminal when the key is moved to start, and then address any remaining starter issues.