I’m working on a truck that tried to start itself while it was raining the other day.

The solenoid on fenderwell was not working. 12v to the trigger wire did not close the circuit.

Replaced solenoid and truck starts normally now.

Not convinced I’ve solved the ghost-starter though. Thinking it’s possible starter running with truck in gear (drove itself across the yard!) cooked the solenoid?

So, I checked voltage to trigger wire on solenoid. 12v (battery voltage) when starting. But, I was surprised to see 9.xx volts with key OFF! I checked another 99-01 truck I have here and it was 4.xx volts with key off.

Not what I expected!!

The GEM and fuse box are dry and no evidence they have been wet.

Whats going on here????

 

I checked mine a couple weeks ago for someone here doing some troubleshooting and I was in the 4-5v range also. Right or wrong couldn't say, but does seem to be the norm.

 

You might be seeing phantom voltage with a DMM, use an analog meter and you will probably see zero.

 

While waiting for the fireplace in the living room to heat up and the coffee to kick in, I will see what I can find regarding the starter solenoid and the voltages that should be available at the solenoid.





I have also attached the Starting System Pinpoint Tests in PDF format from the FSM section 303-06B. I know you have the FSM at your disposal, so if you have trouble viewing the PDF, perhaps the version you have will line up with the version I have regarding the sections.

 

There are not many wiring diagrams associated with the starting system in that section anyway. One for the Excursion, gasoline pickup and diesel pickup respectively.

 

 

Might need to call them!

A couple things to add. The pinout test asks ‘...more than 10v?’ My situation is NO.

This is s ZF6 swap truck. I have not looked at that wiring AT ALL. Until now, nothing was suspect there. But, the clutch safety switch is inop....

 

SSJ, I respect your knowledge and experience on these trucks and know that you have seen more of them than me.
I know you checked the GEM and it was dry.

My only input is that I had a customer with a truck burning up starters, went through 3 motorcrafts before we figured out the GEM was cranking them when noone was around. Water intrusion.

Good Luck!

 

This is disconcerting. The idea that this is even possible - I'm going to take a guess and say the clutch switch had been bypassed? The simple wiring diagram I have in my records omits the presence of the GEM or PCM. The basic schematic Sous posted doesn't show anything, but it does suggest the clutch is a single throw three pole switch. I would image the PCM wants to know when it has a start signal. If this is the case and a diode is breaking down then it could allow voltage to flow backwards in the circuit. So the greater question is how is that clutch switch bypassed and what other semiconductor devices are connected to the start circuit? If the GEM is part of the system (for what bizarre reason??) then a drop of water could conduct enough current to trigger a switching transistor.

This has me thinking I need to find a full wiring diagram now, and I need to leave my truck parked in neutral - loving the idea of it driving itself into the livingroom.

 

The truck in question was molested by a hack job of a mechanic. The truck in question was a 4R100 when it was born and is now a ZF6. The truck in question had so many problems with wiring, fitment and mechanical areas that Jason darn near torn it completely down just to get it to run properly.

In post #7 Jason said the clutch safety switch is INOP, so that is one enabler of the ghost truck. You can see the CPP snip from post #5 below.



This is not a common issue (like fuel bowl heater or GPR failure) and I am curious to see what Jason finds, but if you decide to leave your truck parked in neutral, ensure the parking break is up to the task. I leave my truck parked in neutral a lot and did a lot more before fixed the parking brake. It is not a big deal, just take proper safety precautions.

In an effort to get Jason answers to his ghost truck mystery quicker, I have snipped the GEM pinout from the 7.3L PSD Tech Folder. There is also a GEM Pinpoint Test in the tech folder that may be of use.

 

Central Junction Box = GEM

 

GEM is dry and free of corrosion. Verified again after a full day of rain yesterday.

The starter has not engaged without authorization since replacing the solenoid on fenderwell. The customer also replaced the starter, so I guess it’s also possible it had a problem?

I am 100% certain the solenoid on fenderwell was bad. It did not close the circuit when 12v was applied to the trigger wire.

While i I believe the solenoid could have been the cause, my confidence is low because this truck has been a PITA with soooooo many things wrong.

 

This is your problem.

I know I'm being no help here but I can't seem to stop.

 

kbeefy, I am not questioning your terminology, just trying to clear the fog within my mind regarding the terminology.

In the copy of the FSM I have, the GEM and CJB are two different components.

GEM - General Electronic Module
CJB - Central Junction Box

Connector comparison drawings below.

 

Good news. The truck did not catch on fire.

Bad news, starter continued to run after I stopped turning the key this AM. I jumped out and pulled the trigger wire off the solenoid on fenderwell, but the starter continued to run.... As I ran into the garage and grabbed a wrench to remove the battery cables, the wires near the starter began releasing their smoke........

So, my current thought is there is a short between the main battery cable to the starter and the small wire to starter. Since the smoke got out of those wires, I’m going to pull them for inspection anyway. Joy!!